The impression given by painted pottery, murals, and carved monuments in the Maya area is of a highly scheduled existence, marked by periodic and prescribed acts and ritual obligations, especially among the rulers and elites of antiquity. This relationship was mapped out in the very structure of their ancient cities, with wide processional ways leading to soaring pyramidal structures and temples that served as stages for the politico-religious rituals that sustained regal power over the masses gathered there in the grand plazas below. Given this, it is understandable that both professional archaeologists and laypersons alike are drawn to the many civic-ceremonial centers that dot the Mesoamerican landscape. But there is a world beneath this world. Below our feet, below the jungle floor, lies a hidden realm of caverns and caves, spectacular columned galleries stretching beyond the limits of even the most powerful headlamps, rushing rivers in steep-walled canyons, and crystal-clear lakes, eerily still in the murky and musty darkness. It is to these locations that the ancient Maya, both elite and non-elite, went to commune with deities and ancestors, to conduct funerary rituals, to make sacrifice and petition for rain, health, and prosperity. It is also to these locations that a few hardy archaeologists have ventured, seeking evidence of these ancient activities and to understand their meaning and significance. In this volume, we explore a small portion of the ancient Maya world that has been particularly influential in shaping our knowledge of these subterranean the Macal River Valley of Belize.