Don't be afraid of the dark - join us for the month of October for HOLLOW-een at Cave of the Mounds! Anyone who wants to join can for an extra $2 charge per person when buying a ticket when buying a ticket. This includes a reusable cloth bag, 4 crystals/fossils that you will get in a trick-or-treat style throughout the cave! Plus 1 "bonus crystal" if guest is in costume. Purchase at Ticket Desk!