Mystery Cave

Mystery is one of the better decorated caves in Montana. It's up in the Pryor mountains near the border of Montana and Wyoming. We've actually driven past it for years, and finally get the key to explore it in 2006. It's a wet, active cave so there's a lot of flowstone, stalagtites and soda straws. There's also a good amount of calcite crystals. From "Caves of Montana" by Newell Campbell, March, 1978:

"Mystery Cave is near the south end of East Pryor Mountain; the entrance is a small sinkhole lying in a heavily timbered area. The cave lies on Bureau of Land Management land and has been gated to prevent vandalism; keys may be obtained from the BLM office in Billngs. The cave slopes steeply downward from the entrance and then splits in two directions. The most traveled area is an eastward-trending passage that is very large; 25 tp 50 feet wide and 30 feet high. This passage, which is about 400 feet long, contains large piles of breakdown and a few small soda-straw stalactites. The "upper" level of the cave is a maze of about 1,000 feet of interconnecting small passages and rooms, contains many soda-straw stalactites, stalagmites, and flowstone, and is one of the better decorated caves in Montana.This part contains very little breakdown, and most of the passage and rooms are floored with red clay."