The Well House is located on the northern shore of the Lake, abutting the southern slope of Lookout Hill on the southwestern side of Prospect Park. It was the last structure in the park to be built by Olmsted and Vaux, having been built in 1869. It was made of gray stone and brick, and featured a hip roof and a doorway inside a Tudor arch. The house initially contained machinery that powered Prospect Park's watercourse, and at one point, pumped of water into the watercourse each day. The water from the Well House was drawn from a well, which led to the Brooklyn Aquifer. Originally, there was a smokestack behind the Well House, as well as a cistern in front of the building. The machines became obsolete in the early 20th century when Prospect Park was connected to New York City's municipal water system. Subsequently, the tower was demolished and the cistern was filled in. In 2017, it was restored and turned into a composting restroom.