The Egyptian pyramids—especially the Great Pyramid of Giza—are full of hidden passageways and mysterious chambers, and some are still being discovered. Here’s what’s known (and speculated) about secret underground tunnels: Known Underground Tunnels & Chambers 1. Descending Passage (Great Pyramid of Khufu) A steep tunnel that leads deep underground, ending in the Subterranean Chamber carved into the bedrock beneath the pyramid. Its purpose is still debated—some think it was an abandoned burial ch