Shasta caverns is a great way to spend a weekend. It's about a half hour out of redding and well worth the drive. The caves them selves are increible and really worth seeing. I've been on some other tours of other caverns and they generally seem to disappoint.
Shasta caverns does not. They have a long walk way that goes from one cave entrance to another and all along the way your are emensed in a completly dark tunnel surrounded by stalagtites and stalagmites. It's also fairly cheap.
PROS: Caves, Big Scary looking caves, price