Ah, the Traub. Perhaps the greatest motorcycle mystery of them all, the Traub is quite the enigma. Back in the late 60s, a plumber doing work on a Chicago apartment building knocked a hole in a wall and found a motorcycle hidden within. That's some serious Cask of Amontillado stuff right there. Turns out the bike was stolen by the elderly building owner's son just before he shipped off to WWI. He never returned from The Great War and the bike was forgotten.

Thing is, no one knows where the Traub came from. There's no evidence of a Traub motorcycle company, and there's never been another Traub found. It's possibly a one-off garage build, but the engineering and quality of materials are incredibly sophisticated—far beyond the abilities of the average circa 1916 tinkerer. So, some professional somewhere made this thing, but why? Where did the late, lamented bike thief get his hands on it? It's mind-boggling.

The Traub currently lives at the Wheels Through Time museum in North Carolina. Best thing about it? It still runs.