The Amber Room
Gifted to Russia in 1716, The Amber Room was designed by Andreas Schlüter and Gottfried Wolfram. Displayed with a stunning array of amber, jewels, and gilding, this room (that was situated in Catherine Palace, St. Petersburg) was considered by many to be the 8th wonder of the world.
When the German army marched nearer to St. Petersburg during WWII, the Russians hid the room in layers of wallpaper and decor. However, the Germans found it, disassembled it, and shipped it off to Germany. Historians can’t seem to agree on whether or not it was lost to bombardments or theft. Regardless, the room is still considered to be lost to history, despite the fact that there have been verified remnants of it found as recently as 1997.