"THE CAVE"

5 STAR Kid Cache!

Batman's BatCave

Prepare to get wet!! This one definitely raises the bar for the Rohnert park Geocachers. Certainly not a 5x5 though. 
A more realistic rating would be a 1.5x3 but since it does require a flashlight (tool) and wading - or flotation device for people with a height disadvantage, the rating may actually apply.

Be Like an Aussie...

Big Yawn

What a blast! This one's difficulty is not only due to the question of how do access the hide, getting there and finding the well hidden container is a fun challenge. The path is cramped for those taller than 5'5" or so, so it might be wise to wear a helmet, right Geojammers? ;-)

C.H.U.D

Could sure use some CITO but a fun spot none the less.
This one requires one to pretty much crawl into the access but then opens up into a nice roomy shaft. It's doesn't go in very far and there may actually be someone living in the back. Go in groups for safety and prepared to get dirty.

CAVE MAN

Cavewall

Chrissy's Cave

Courtnie's Cave

Wow.. Our first horizontal mine!

This one is not very easy to locate unless you follow the cache owners description but there is an alternative approach. Both require the same steep descent to the adit. A more accurate rating would be a 1.5x3.5 as the water level is rarely above the knees and the container is in plane sight - if you're looking! The current difficulty rating of 3x5 can easily be justified as you do need a flashlight and wading is required.

Down to a Sunless Sea

While we have not completed this Wherigo, we have been to stage-1 which requires sliding/crawling into a dark, dank mine. Not a long mine shaft but fun to explore. Ratings for this complete wherigo are 100% accurate.

Frodo's Quest

More of a rock grotto cave, more difficult to find than to access. None the less, a fun adventure that will test your arachnophobia :-) Fear not, although some claim to see Black Widows, our thorough inspection showed nothing more than the usual cave spiders.  Will require crawling and can be damp. One very nice thing about this one is the trail to GZ from the parking area.

Hell Hole?

HORSESHOE CAVE FOR FRIENDS

I Pack a Chainsaw: The Big Deep

Into the Beyond

Into the Night...or Into the Light....

Konocti Caverns

Well, this one actually doesn't really qualify but it does take you to the adit.The mine beyond is clean and while it has caved in about 100 feet in, a joy to explore.

Mine Shaft

My One and Only Storm Drain Hide

Pandora's Box

This list is of caches known to have you visit a cave, mine or underground tunnel of some sort.

If you know of a cave cache, tunnel hide or any other kind of underground hide in California that is not on this list, please let me know!

It's possible that I have not added one after viewing the page description and/or speaking with the cache owner as some are meant to stay a mystery for difficulty ratings.

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Underground, cave, mine or tunnel hides in CAPublic