Since the World’s Fair of 1867, Parisians and international visitors have ventured into the subterranean world that exists below street level to discover the mysterious inner workings of the city’s sewers. Nearly a century later, the Paris Sewer Museum opened in 1975, and has expanded since then. Today, fresh off its latest renovation, the museum’s entrance is housed in a modern new building, and visitors have improved access to the sewer galleries and exhibition spaces, which detail the sewers’ construction, history, and maintenance. It’s advised to book tickets online in advance of your visit, as only a select number of people are admitted into the museum at any given time.