A National Historic Engineering Landmark, this beautiful Greek Revival complex was built in 1815 and pumped water from the Schuylkill River for the city's consumption until 1909. It was one of Philadelphia's biggest tourist attractions in its day and is still well worth a visit for its excellent interpretative center, where you can learn about the pumping station's history, the area's natural history, and conservation of water resources and the environment.
See the website for various guided tours of the center and around the park.