Sioux Falls is a city in South Dakota. The Big Sioux River tumbles over a series of rock faces in Falls Park, which includes an observation tower and the ruins of the 19th-century Queen Bee Mill. The Queen Anne–style Pettigrew Home & Museum has artifacts collected by Senator Richard F. Pettigrew. The Old Courthouse Museum offers exhibits on local history. Southwest, Sertoma Park has a butterfly house and an aquarium.