In the 1950s, they were functioning sand filtration silos with underground catacombs with sand banked knee-high at the corners. In 1987, they were long abandoned and sold to the District, where they would sit for thirty-seven years as nothing more than a spot for DMV urbex. In 2024, they were renovated into a public park for families— and not only that, but a sand silo-themed playground.

If urbex is nothing more than a playground for grunge adults, McMillan Reservoir is a rare success story. After over three decades of decay, it would have been a typical urbex storyline for the park to be bulldozed to make space for something new and clean. Instead, the district chose to preserve the silos and catacombs. As quoted in this Washington Post article at the time of the renovation:

It gives the 6.2-acre park somewhat of an otherworldly feel, an unlikely cross between industrial and recreational. From the indoor pool, you can peer through the glass windows into the eerie catacombs, which once held sand for the city’s 20th-century water filtration system. The city leaned into the theme: The playground has a sandpit, a slide that pays homage to the shape of the silos, and a miniature play “regulator house” that mimics the brick control rooms next to the old sand towers.

To visit, you can enter McMillan Sand Filtration Site into your GPS. It's located at the corner of Michigan Avenue and North Capitol Street in Washington, D.C.

If you're looking for a way to explore some underground tunnels that aren't illegal (imagine!), there's no better place than the Pedway. Chicago has a huge network of connected paths that will take you almost anywhere in the business district. Click here to see where it can take you - and enjoy traveling through a less-crowded, less-frigid Chi-town! (Disclaimer: Pictures above aren't mine... I ended up just taking video footage. See below!)

A lot of universities have underground tunnels built to allow students to walk between classes in subzero temperatures. Northwestern isn't one of them. Our tunnels are strictly off-limits to students, but that doesn't stop literally everyone with a taste for adventure and an iPhone from finding their way down at one point or another. Walking through these can take you from the observatory on North Campus to Fisk Hall on South. It's also insanely hot... and incredibly cramped.

The easiest access point is an air vent outside of the observatory. Make your way to the green, tent-shaped cover hidden behind the row of bushes and pull it off to reveal a ladder down into the tunnels. Be very careful not to touch any uncovered pipes with your hands or you will be burnt! If you are sneaky enough, you can climb down the pipes without hurting yourself and get onto the ground into the first tunnel, pictured above. From there, keep walking until you reach the end or leave through one of the many other access points. Remember to close the one you went through on your way in!