Substrate

The deeper you go, the hungrier it gets.

Beneath the parched crust of the Nevada desert lies the Aos Si cavern system-a jagged, uncharted fissure that has beckoned cartographer and extreme caver Kaelen Rigg for years. With a hand-picked team of specialists, including geologist Dr. Aris Thorne and survivalist Liam O'Connell, Kaelen descends into the dark, eager to map the unmappable.

But Aos Si is not like other caves. The squeezes are impossibly tight, forcing the team to exhale just to inch ...