This is not a TripAdvisor Top-10 list you want to be on. Runner-up status for world’s germiest tourist attraction goes to Seattle’s Gum Wall in Post Alley, second only to Ireland’s Blarney Stone. It’s a form of people’s participatory art apparently started by improv Market Theatre-goers in the early 1990s, who thought better of sticking their gum under seats and started leaving it on the brick wall outside. Over the years, it’s grown vertically, horizontally and now is spreading to the wall on the west side of the alley, with gum stuck to the signs requesting “No Gum This Side, Thank You.” The Pike Place Market estimates the wall holds 750,000 wads of gum. The Gum Wall beat out Paris’ sewer tour and India’s Karni Mata Rat Temple.