Cutta Cutta Caves, Australia

In Nitmiluk National Park in Australia’s Northern Territory, visitors can take a one-hour guided tour of the Cutta Cutta Caves with Nitmiluk Tours (phone +61 08 8971 0877, www.nitmiluktours.com.au). 

Carved naturally from limestone over millions of years, the cave system is nearly six square miles in size and is home to five species of bats. On a walkway with a railing, tours depart hourly, 9 a.m.-3 p.m., and cost AUD22 (near $16) per person; book in advance. Nitmiluk National Park is about 17 miles northeast of the city of Katherine via a private road.