Built in 1869, this building sits beside a well that once pumped about 750,000 gallons of water per day into a nearby reservoir, which in turn fed the park's artificial watercourse (all the bodies of water in Prospect Park are man-made). When Brooklyn became part of New York City in 1898, it gained access to the city's water supply system, and the well and reservoir were no longer needed.
That’s a bit of trivia that is something I did not know.