Almost 80km up the river from Fort Albany, Ontario
Once you fly to Fort Albany and convince someone to pilot you up the river, you're in for quite the trip! Alternately, you could Start up river a few hundred km and go with the flow to the cache... prepare for a 3 week trip! 

4.5lb Walleye

Why not visit Alert, NWT for a little Geocaching Milestone?

As North As It Gets!

NE of Madoc, Ontario, near Lingham Lake
30km round trip to trailhead. After a short 8km drive down a 4x4 road, and visiting GCGQHP - Lingham, take the ATV trail to the left and head for the cache... you can't miss it! he he, yeah. This one was FUN!
FOUND BY MTB

Bushwacker

Mount Everest, Iibet, China
Who's up for a quick climb to the top of the world?

Chomolangma

Härryda, Sweeden
Micro Cache hidden on the support beam of a highway bridge. Access is straight forward if you are not afraid of heights, or falling!

Deathwish?

Devon Island, Nunavut, Canada, at NASA/CSA research camp near 20km Haughton impact crater.

End of The World

Fly-in fishing outpost 65 miles NE of Red Lake, Ontario
Fly-in you say? This may take a while to arrange... but I'll be watching!

Ghost Cabin at Loon Haunt

Remote Alaska, Not Found Yet - Tied for Oldest Unfound Cache

Kougarok

Final stage requires entry and decent into a "Hot Zone". Radiation and particulate protection is required.

Psycho Urban Cache #9 - Hot Glowing Tribulations

Houston, Texas, USA
Once you find the Dead Drop and visit the Bunker, who knows where your adventure will take you!

Quantum Leap

Hydrothermal Vent at the sea floor 2300 meters down in the Atlantic Ocean

Rainbow Hydrothermal Vents

Day hike up the Spooky Canyaon. Be prepared to deal with poisonous snakes, flash flooding and other hazards.
Mammoth, Arizona, USA

Spooky Canyon

This is a cache that is extremely difficult to get to, and then once in the area, the cacher must leap over a deep crevice to reach the cache box. Thus far, it's been a lonely destination. Flagstaff, AZ

The Leap

South side of lake Monroe, Ontario
Float Plane eh? I'll have to work on that one...

They Would Have Loved It

Germany (town of Gleisweiler) - Waterfall (Shower)

Walddusche

Saganaga Lake, Canadian Side
Remote wilderness. Border crossing permit required!

Wherever I May Gnome

Near Lake Superior Provincial Park, Ontario
Ride the Algoma RR to mile 122 1/2
With the exception of GO Caches... this is the only one I know of that requires you to TAKE the train! I'd love to come for a visit.

Woody's Windy Wanderings

These caches present an extreme challenge in reaching the cache location. Specialized equipment is almost mandatory, and  a 5/5 Terrain rating is expected...

These are the caches everyone dreams about finding!
Good luck!

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