Over the millennia, as dozens of swift-flowing rivers bored through the soft limestone, the Maya Mountains became pitted with miles of caves. The Maya used them as burial sites, and, according to one theory, as subterranean waterways that linked the Cayo with communities as far north as the Yucatán. Previously, the caves fell into a 1,000-year slumber, disturbed only by the nightly flutter of bats. In recent years, the caves have been rediscovered by spelunkers.
Caves Branch Adventure Co. & Jungle Camp. First on the scene was Ian Anderson of Caves Branch Adventure Co. & Jungle Camp. He and his friendly staff of trained guides run exhilarating adventure-theme caving, tubing, and hiking trips from an upscale jungle camp just south of Belmopan. They also run day and overnight kayaking trips in the Cayo District. 12 mi [19½ km] south of Belmopan, Mile 42 1/2, Hummingbird Hwy., Belmopan, Cayo. 866/357–2698. 610/3451. www.cavesbranch.com.
PACZ Tours. Arguably the best Actun Tunichil Muknal tour operator, PACZ has been operated by Emilo Awe since 1998, with help by Bob Jones, formerly of Eva's, and about eight tour guides. The ATM tour costs around BZ$220 from downtown San Ignacio—including lunch and ATM admission, if you book directly with PACZ. Your hotel or lodge can arrange an ATM or other caving trip but may add an additional fee. 30 Burns Ave., San Ignacio, Cayo. 824/0536. www.pacztours.net.