Seattle Underground, Washington
Beneath the city of Seattle is the ghost town of, well, Seattle. In the aftermath of the Great Seattle Fire of 1889, which decimated the city's entire central business district, it was determined that the best way to rebuild would be to do so one story higher. Which meant that an entire collection of business storefronts had literally been buried underground when new sidewalks were constructed.
Or at least that was the rumor. As part of his efforts to save Pioneer Square, Seattle Times columnist-turned-historian Bill Speidel set to determine the veracity of these claims. It turns out they were true. In 1965, Speidel and his wife, Shirley, conducted their first subterranean tour of what was once the city's ground level. And though Speidel passed away in 1988, the tours continue on a daily basis today.
Getting there: Bill Speidel's Underground Tours kick off every hour on the hour daily in Seattle's Pioneer Square. (They begin at Doc Maynard's Public House, an underground – and restored – 1890s saloon.)