A Prospect Park building out of use for nearly 100 years will open to the public on Monday as the site of several new composting toilets, according to the Prospect Park Alliance.

The four toilets — three for women and one for men — sit in the Wellhouse building near the northern shore of Prospect Park Lake. The building was constructed in 1869 and the last remaining building by the park’s designers Frederick Law Olmsted and Calvert Vaux. It originally housed the mechanical systems that pumped water into the park’s waterways.

The project cost $2.34 million, which covered the installation of the toilets and as well as the preservation of the Wellhouse building, according to the alliance.

While the human waste will take years to compost— and reportedly cannot yet be used as fertilizer in New York — the new toilets are expected to use 97% less water than traditional toilets, according to the alliance.

And don’t worry about the smell: The composting facilities are all stored underground.

The new restrooms join the park’s seven other facilities scattered throughout the 526-plus acres.