Image courtesy of Dupont Underground.

Tickets are now available for the first art installation in the Dupont Underground, but they’re going quick—after one day on sale, the first week is entirely sold out.

The exhibit, called Raise/Raze, was designed by New York-based firm Hou de Sousa. The studio won the Re-Ball! competition, which required using the more than 650,000 balls from last summer’s National Building Museum’s exhibition of The Beach in an entirely new project.

Raise/Raze features the balls glued together to form building blocks for five different zones underground, which visitors can take apart and put together using velcro. “Raise/Raze is like sand in a massive sandbox. It is a medium for communicating ideas and building objects that is intuitive and easy to use,” says Dupont Underground in a release.

The underground space has an occupancy of 49 people at a given time, which helps explain why the tickets are going so fast.

The installation will run from April 30 and run through June 1. Tickets cost $16.82 and are available here.