During the California heat wave of 1906, Baldassare Forestiere dug a home underground with just a pickax and shovel. He spent 40 years excavating 10 acres of rooms, tunnels, a chapel, an underground aquarium, and courtyards to experiment with underground farming. With no budget, he mixed mortar from the dirt he dug out, creating his own concrete and bricks. Despite continuing to work as a day laborer during the day (mostly digging irrigation ditches), by the 1920s, he had completed about 50 subterranean rooms.

A Sicilian immigrant to Fresno, California, Forestiere had planned to farm citrus until discovering that his 80 acres of hardpan soil were unusable for planting. Digging as far as 20 feet below the surface, Forestiere reached depths wher...