Go to Platina on Highway 36; be sure to give friendly waves to any cars or trucks you pass. After grabbing a burger and onions rings at the Platina General Store, turn left onto service road 29N06. Head into Shasta-Trinity National Forest. Disregard the lack of pavement--it doesn't matter. 29N06 swings right past the Eastern Orthodox Monastary, where the St. Herman of Alaska Brotherhood think deep thoughts amongst the trees.
Just a little past the monastary (or a little before--it's been a while), you may see a large boulder on the left side of the road. From an overhang above the boulder, ferns and moss drip moisture onto the boulder's top, but the top is above eye level. Where's all that water going?
And if you are intrigued enough, and not in any real hurry, you can stop and climb the boulder to investigate. And you'll see that the top of the boulder is hollow, and a clear pool of water has collected, shadowed by cool ferns and moss even in the summer. Water striders live in the poool, and perhaps even other animals.
Cliff Prettie showed me the boulder.