Several weeks back Nicole and the kids went on a homeschool field trip to Cave-In-Rock in southern Illinois. According to Wikipedia it was "worn into the sandstone bluffs of the Ohio by river floods, especially during the meltoff following the Wisconsin ice age." Here are some pictures of the ferry ride over and of the cave.
They also went to a mineral museum in Marion, KY. Obviously they got to learn about rocks/minerals but they also learned about mining and history of mining in the area. Here are some pictures.