The Caves Branch River carved its network of subterranean passages through Belize's limestone plateau over two million years, long before the Maya established ceremonial centres in the Cayo District. By the time Xunantunich and Caracol rose above the jungle canopy, these underground rivers had already hollowed out cathedral-scale chambers and polished their walls smooth. The Maya recognized the caves as xibalba—portals to the underworld—and left behind pottery shards, ceremonial altars, and skeletal remains that archaeologists continue to study today. Cave tubing from San Ignacio emerged as a recreational activity only in the 1990s, when former Special Forces medic Ian Anderson converted his family's jungle property into the first cave-tubing concession. Within a decade, the Caves Branch Archaeological Reserve had formalized access protocols, and the 20-dollar conservation fee now funds ongoing site protection and guide training. San Ignacio sits seventeen miles east of the Guatemalan border and serves as the logical staging point for cave tubing tours departing toward the Caves Branch region. Most operators run morning convoys along the George Price Highway, reaching the Mile 37 trailhead by 09:00 to avoid the midday heat that turns the jungle approach into a steam bath. The limestone karst topography that defines the Cayo District creates ideal conditions for cave formation: rainwater absorbs carbon dioxide as it percolates through soil, forming weak carbonic acid that dissolves calcium carbonate over geological timescales. The result is a maze of subterranean rivers, collapse dolines, and galleries hung with stalactites that predate human presence in Central America. Modern cave tubing from San Ignacio tour itineraries typically pair the float with secondary adventures—zipline canopy circuits, Mayan ruin climbs, or Barton Creek paddle segments—because the tubing portion itself lasts only ninety minutes of drift time. The Caves Branch system remains active hydrology; during the rainy season, from June through November, water levels rise and current speeds double. Guides monitor flow rates daily and reserve the right to cancel when subterranean passages flood beyond safe clearance. The caves themselves maintain a constant 22 degrees Celsius year-round, a full six degrees cooler than the external jungle, and the darkness inside is absolute once headlamps switch off. Bats occupy the upper reaches, and freshwater crabs patrol the shallows where light penetrates from collapse openings overhead.