Samwel Caves is located on the uppermost McCloud arm of Shasta Lake in Northern California. This cave system has a little of everything for the do it yourself cave explorer including plenty of danger. Legend even has it an Indian Maiden fell to her death in a room that has a 90-foot deep hole.
The caves are accessed with a key that is checked out from the Shasta Lake Ranger Station in Mountain Gate. You can download a pdf guide for the cave at Spelunkers Guide To Samwel Cave.
Samwel Caves has a lot to offer claustrophobic, and people prone to hitting their heads. If you fall into one of these I would advise being prepared to crawl, and bust your head more times than you can count.
You may not put Samwel Caves on the list of yearly activities, but this is a nice outing that is free and somewhat exciting.