The Winchester House
If this "mystery house" isn't actually haunted— and the U.S. Department of Commerce has certified that it is— it's still one of the spookier construction projects in history. After the death of her husband and child, Sarah Winchester (the wife of the rifle-maker's son) consulted a seer who proclaimed her family had been killed by the ghosts of those who died of bullets from her family's guns. The seer suggested that only perpetual construction on the family's mansion could mollify these spirits. So that's what Sarah Winchester ordered. Workmen labored on the property every hour of every day for 38 years. The 160-room estate, built entirely without the aid of blueprints, is truly bizarre: some of the creepier features are staircases to nowhere, doors that open onto brick walls or ten-foot drops, and a window with an etched-glass spider-web motif.