R'lyeh

Pioneering beavers have found a strange, abandoned city. The old buildings stand rusted, though many of the bridges stretching strangely and impossibly across the gaps still stand pristine. Trees and berries still grow in cultivated patches, and yet... no one, hooman or beaver, remains. The only clues to the fate of the strange, impossible city are massive pools of contaminated water almost shaped like... footprints.