One of the most offbeat attractions in the United States, the Seattle Gum Wall is also one of the most germ infected tourist spots in the world.
Located in Post Alley, under Park Place Market, the Gum Wall has its beginning in the early 1990s, when people, irritated that they had to wait in line to get tickets to the theater, stuck chewing gum on the wall. At first, they would use the gum to stick small coins to the wall, but in time, the tradition of the coins disappeared, and the gum remained.
Theater attendants scraped the Gum Wall twice, but gave up in 1999, when it became a certified tourist attraction of Seattle. Now it's filled with thousands of pieces of chewing gum, of any color imaginable. Be warned, however - The Seattle Gum Wall is also one of the germiest tourist destinations on Earth.