This is the acclaimed “Cave of the Crystal Maiden,” one of the most spectacular natural and archaeological attractions in Central America. The trip to Actun Tunichil Muknal, or ATM as the cave is also known, is for fit and active people who do not mind getting wet and muddy—and who are able to tread lightly around ancient artifacts.

After the initial 45-minute hike to the entrance (with three river fords) and a swim into the cave’s innards, you will be asked to remove your shoes upon climbing up the limestone into the main cathedral-like chambers. The rooms are littered with delicate Maya pottery and the crystallized remains of 14 humans.

There are no pathways, fences, glass, or other partitions separating the visitor from the artifacts. Nor are there any installed lights. The only infrastructure is a rickety ladder leading up to the chamber of the Crystal Maiden herself, a full female skeleton that sparkles with calcite under your headlamp’s glare, more so during the drier months.

Please be careful—the fact that tourists are allowed to walk here at all is as astonishing as the sights themselves (at the time of this writing, somebody had already trod on and broken one of the skulls). Only a few tour companies are licensed to take guests here; Pacz Tours (tel. 501/604-6921 or 501/824-0536, www.pacztours.net) is the most popular provider.

The Actun Tunichil Muknal cave is neither for the weak at heart nor recommended for small children or claustrophobics. In fact, children under the age of 8 (or 12, depending on whom you ask) are not permitted inside. Entrance to the site is US$25 per person.