When: Sept. 1-Oct. 31, 9 a.m.-4 p.m., $5-$10. Onondaga Cave State Park, 7556 Highway H, (seven miles southeast of the I-44 Leasburg exit), Leasburg, 573-245-6576, http://www.mostateparks.com/onondaga.htm.
Trained guides lead visitors over almost one mile of electrically lighted, paved walkways and provide information about geologic wonders within this National Natural Landmark. Tours last just over an hour; the cave is 57 degrees year-round.