To call Washington a "swamp" is a metaphor, but also the literal truth. So, when planning began for the Lincoln Memorial in the early 1910s, builders faced a real sinking problem. Their solution led to one of Washington's best-kept secrets, hidden for over a century … until now. Underneath the Lincoln Memorial is what's known as the memorial's Undercroft (a term usually reserved for the vaulted basement of a medieval castle or cathedral). Here, 120 massive concrete pillars sink 50 feet into the