When you find a cave, it’s natural to assume some combination of geological processes carved it out. But what if you’re really standing in the burrow of an ancient giant with the digging skills of a gopher? That’s the realization some scientists had when they stood in odd tunnels in southern Brazil. Rounded with smooth floors and claw marks along the wall, the caves may have been dug out by elephant-sized giant ground sloths or maybe a species of enormous armadillos, both now long extinct, Discover Magazine reports. Whatever the responsible critter, next time you’re out adventuring underground, you might think twice about whose home you could be exploring.