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Zadar Sea Organ — Geocache of the Week

Traditional Cache
by donweb
Zadar, Croatia
N 44° 07.012 E 015° 13.223

There aren’t many places in the world where you can watch a burning sunset over the sea, listen to soothing organ music, and then be treated to a solar-powered, galactic light show…without moving from your spot the whole time.

In fact, there’s probably only one place on earth where that’s possible. And there’s a geocache there.

Zadar waterfront from above.
Zadar waterfront from above.

The Burning Sunset

Croatia’s sunniest months are July and August. Luckily for visitors the sun tends to set every day, so views like this can happen year-round.

Tall ships are a frequent sight.
Tall ships are a frequent sight.
A perfect shot.
A perfect shot.

Soothing Organ Music

The amazing sculpture/instrument known as the Sea Organ (Croatian: Morske orgulje) is made up of a series of differently-sized tubes located in the water underneath a set of large marble steps. The movement of the waves rushing across the tubes creates beautiful, if a bit random, music.

Tubes hidden underneath marble steps produce organ sounds as the waves flow across them.
Tubes hidden underneath marble steps produce organ sounds as the waves flow across them.
One of the organ holes.
One of the organ holes.

Galactic Light Show

At the top of the Sea Organ stairs is another installation fighting for the title of Most Futuristic. Embedded in the ground are approximately 300 glass solar panels called the Sun Salutation, which are perfectly walkable by day.

At dusk, the Sun Salutation switches on and displays a series of bright and colorful lights. The motion of the lights depends on the solar energy collected throughout the day as well as the power of the waves, and mimics the motion of the solar system. All eight planets are represented by solar lights placed at their proportional distances from the sun. Both the Sun Salutation and the Sea Organ were designed by the architect Nikola Bašić.

A series of solar panels arranged in a circle light up at night.
A series of solar panels called the Sun Salutation light up at night.
A sunset, the Sun Salutation lights begin to glow softly.
A sunset, the lights begin to glow softly.
The Sun Salutation makes a great dance floor.
The Sun Salutation makes a great dance floor.

All this, and of course there’s a geocache nearby to find. GC322MF is a popular meeting point for visiting geocachers who host events. The cache has 136 favorite points, and while the cache itself might be your run-of-the-mill hide, the things you’ll find when you reach it are truly incredible. 

The cache.
The cache.
An energetic moment captured on camera by geocacher cdem62.

Continue to explore some of the most amazing geocaches around the world.
Check out all of the Geocaches of the Week on the Geocaching blog. If you would like to nominate a Geocache of the Week, fill out this form.


Return of Challenge Caches

Today we’re happy to announce the end of the moratorium on challenge cache submissions. Effective immediately, new challenge caches may be submitted in accordance with the updated guidelines.

Challenge caches encourage people to set and achieve fun goals. There’s no doubt that they’re a beloved part of the game for many geocachers. However, challenge caches represent a major exception to a basic guideline: For physical caches all logging requirements beyond finding the cache and signing the log are considered additional logging requirements (ALRs) and must be optional. Geocaching HQ has long exempted challenge caches from this guideline because they can bring so many positives to the game.

With that exception comes an expectation that the negatives won’t outweigh the positives. Unfortunately, a number of negative factors led to the moratorium going into effect last year, including:

Subjectivity often results in a difficult review process. Reviewers are volunteers who give their time to support the geocaching community. With most cache submissions, it’s usually pretty clear to reviewers whether a geocache is publishable. But challenge caches are different. Many reviewers cite the sometimes contentious process of reviewing challenge caches as the least fun thing about reviewing. Since each reviewer examines hundreds or thousands of cache submissions each year, we (HQ and the community) owe it to them to make the process as enjoyable as possible!

High percentage of appeals to Geocaching HQ. Cache owners can appeal a reviewer’s decision to HQ if a cache submission is deemed unpublishable. We found that more than 50 percent of appeals related to challenge caches prior to the moratorium. That’s despite the fact that less than one percent of cache submissions were challenge caches. It was another sign that the challenge cache system wasn’t working.

Logging requirements are often misunderstood. Some challenge caches are very simple for cachers to understand. However, more and more we found people were submitting challenges with very long lists of logging requirements. In some cases, a single challenge cache listing totaled multiple pages when printed. Appeals for such caches often resulted in the kind of back and forth that can make the process very difficult.

These were among some of the known drawbacks to challenge caches. A big goal of the moratorium was to gain an even deeper understanding about what the community and volunteer reviewers liked and didn’t like about challenges. We also wanted to hear your suggestions for how to improve challenge caches. Hundreds of geocachers took part in our User Insights Forum. Nearly 20,000 of you also completed our survey on challenge caches. With all of that data in hand, we set about building a framework that we hope will allow challenges to continue and thrive.

What’s Changing?

Challenge checkers. Perhaps the biggest change is that all future challenge caches must include a web-based challenge checker. We began looking at this idea after it was suggested by many community members during the User Insights Forum. We then found that a high percentage of survey respondents favored the idea. Checkers will make it much easier for caches to know whether they qualify for a challenge.

Since Project-GC is already very experienced in hosting challenge checkers, it made perfect sense to work with them to officially integrate checkers into new challenge caches. Read more about challenge checkers in our Help Center. (We want to thank Magnus and his colleagues at Project-GC for their partnership in this process!)

Guideline changes. We’ve updated both the format and some content in the Challenge Cache Guidelines. Here are some of the more important updates:

CO is required to have qualified for the challenge. This change was heavily supported in the community survey. In the past, some COs submitted crazy challenges for which even they could not hope to qualify.

Time-limited challenges are not permitted. For example, “Find 500 caches in a month” or “Find 10 different icons in a day.” The aim here is at least two-fold. First, these challenges encouraged people to hurry to find caches in a short time period. That’s something a majority of survey respondents said they didn’t like about challenge caches. And it’s not something we wish to encourage. Second, we’ve seen a lot of people creating Events and/or CITOs only to add an icon to the area for “Busy Day” challenges. That’s not at all the spirit for which those activities are intended.

Streak challenges limited to 365 days. Ask an experienced cacher, “What did you like most about your caching streak?” and the common answer is, “The day it ended!” Finding caches every day for a long period often makes caching feel like a chore. But we didn’t want to restrict them completely, so we’re setting a maximum streak length for challenges.

No challenges based on Waymarking, Benchmarking or Trackable logs, or specifying Lab Cache finds. The community survey results showed low approval ratings for challenges involving these things. While many geocachers do enjoy Waymarking and Benchmarking, these activities aren’t geocaching. Challenges involving trackables can lead to mass logging and other behaviors that aren’t ideal for TBs.

We are not permitting Lab Cache challenges because Lab Caches are temporary, are generally only available to those who attend Mega- or Giga-Events, are not associated with Found It logs, and are not completely integrated into Geocaching.com stats. However, since they are included in user profile stats for Total Finds, Longest Streak, and Finds for Each Day of the Year grid, we are making an exception to permit Lab Caches to be used as qualifiers for challenges related only to those metrics.

Challenges cannot be based on these listing elements: cache titles, cache owner names, GC Codes, or listing text. This would include such challenges as “Find a cache for every letter of the alphabet” or “Find caches with the Periodic Table symbol in the GC code.” They generally reward database management, rather than geocaching achievement. More importantly, they often lead people to place caches whose titles start with a certain letter or contain a specific word, only to help people qualify for challenges.

What’s Not Changing (for now)

The idea of a challenge cache icon or attribute earned significant support from the community. We agree there are a lot of good reasons to implement one. However, we want to confirm that the new framework will reduce the problems which led to the moratorium. It wouldn’t make sense to engineer a new icon or attribute only to lose it if challenge caches don’t work out. We’re going to give it a year or so, and then re-evaluate the situation. If we find that things are going well, then we will strongly consider adding a new icon or attribute for challenge caches.

What’s Next?

We love how challenge caches encourage people to set fun goals and expand their caching horizons. There’s no question we want these caches to thrive for years to come. We have high hopes that this new framework for challenge caches will reduce some of the pre-moratorium difficulties for reviewers and the community.

But challenge cache owners are integral to the success of this framework. It’s important that they work within these guidelines in order to reduce the burden that reviewers felt prior to the moratorium. If after a period of evaluation we find that a lot of the pre-moratorium issues are still causing problems, then we’ll know that this new framework isn’t the answer. We don’t have a backup plan. The only remaining option would be to not permit challenge caches as they currently exist.

But we’re hopeful the community won’t let it come to that. Through your participation in our User Insights Forum and survey, geocachers and community volunteer reviewers have eagerly participated in a comprehensive process that has resulted in what we believe is solid framework. We’re happy to know that challenge caches will continue to inspire people around the world to achieve exciting geocaching goals!

Read more:

Challenge Cache Guidelines

Learn about Challenge Checkers

Challenge Cache Subjectivity


7 Tips for Finding your First Scuba Cache

You’ve dominated the game on land and now you’re ready for the next level of geocaching — sea level that is. Dave from Geocaching HQ, aka HiddenGnome, recently found his first scuba cache in the US Virgin Islands. He returned to HQ with a plenty of vitamin D and some great advice for those who also want to go on their first underwater geocaching adventure. Scuba caches are no easy feat, but with these 7 tips from Dave, you’ll soon be ready to take the plunge.

Dave himself finding his first scuba cache, GC3CMHE, in the US Virgin Islands

1. Get certified. Before attempting, make sure you have proper scuba certification.

Geocacher "FJFitzgerald " at GC1D6ZQ in Michigan.
Geocacher “FJFitzgerald ” at GC1D6ZQ in Michigan

2. Read cache details carefully as every scuba cache is different. Some will require park entrance fees while others may ask you to notify the local park ranger.

Geocacher Peter_U and friends at a underwater cache site in Finland
Geocacher Peter_U and friends at a underwater cache site in Finland

3. Research the diving area and its ecosystem. You don’t want to be unpleasantly surprised by the local sea creatures or water temperature.

Geocacher "Stray65" at GC3GB52 in Egypt
Geocacher “Stray65” at GC3GB52 in Egypt

4. Bring a compass. GPS devices will not work underwater but a compass will help you navigate while submerged in water. You can also triangulate the position of the geocache based on provided landmarks – certain cache listings will specify.

Bring a compass for navigating

5. Buddy system is a must. In the off-chance that something were to happen (an underwater current), you want to make sure someone knows where you are.

Travelingeek and friends at GC4BAC0 in Cayman Islands

6. Bring a pencil or waterproof writing utensil to sign the logbook. Standard pens won’t work when wet.

Logbook at GC34AAB in Mallorca

7. Carry an underwater camera… so you can snap a shot of yourself finding the cache!

Say cheese!
Say cheese!

What other questions do you have about scuba caching?


HCue: How To Make a Hollow Book Geocache

Do you consider yourself a book nerd and a geocaching connoisseur? If yes, then this HCue video was created just for you. Grab yourself some glue, a few cutting tools, and a thick book (of witchcraft and wizardry), and you’ll have all of the necessary tools to create your own “Chamber of Secrets!”

What You’ll Need:

  • Thick Book – Make sure it’s large enough to fit a logbook, Trackables, and other geocaching trinkets
  • Box Cutter or X-Acto Knife*  
  • Saran Wrap
  • Straight-Edge Ruler
  • Pencil or Pen
  • Power Drill – Optional but very helpful
  • White Glue/Water Mixture  – 70/30 ratio mixture
  • Paint brush
  • Band-aids… Just in case


  1. Select a page near the beginning of the book and use Saran Wrap to cover that page, the pages before it, and the front cover. This saved page will be used later on in the process.
  2. Firmly hold down the remaining pages and brush the outer edges with the glue/water mixture. The Saran Wrapped pages should be protected from the glue mixture.
  3. Place some sort of heavy object on top of the book and wait for the glue to dry. This should take around 15-30 minutes.
  4. After the glue dries, open the book to the first glued page. Draw 1/2 inch border inside the page edges using a writing utensil and ruler.
  5. If you have a power drill, drill a hole in each corner of the border. Using the ruler and cutting tool, start carefully cutting through the layers. Safety always comes first (as you saw in the video) so take your time cutting!
  6. Cut until you reach the back of the book. Do not cut the back cover. Then remove stray paper debris.
  7. Brush the inside edges and top of of the cut-out pages with glue/water mixture.
  8. Carefully remove the Saran Wrapped pages that you set aside step #1 and placed the saved page right before the cut-out pages onto the wet glue mixture.
  9. Close book, add weight, and let dry for another 15-30 minutes.
  10. Cut through saved page.
  11. Your hollow book geocache is now complete! You know what to do from here. And if you don’t, go here.**

*These should only be used by adults with experience handling these tools.

**These containers are placed commonly in libraries and other wonderful “book-filled” environments.