Niagara Cave
Harmony, Minnesota
No bats, but Niagara Cave does have a 60-foot-high waterfall that you view from a bridge (kind of like the real Niagara Falls, only underground), plus a wishing well, echo chamber, and "Paul Bunyan's bed," among other formations. The largest limestone cave in the Midwest; open as an attraction since 1934. Over 400 weddings have been performed in Niagara Cave's subterranean Wedding Chapel.