Walk, jog, bike, fish, play basketball, walk your ferret, have a picnic. It starts up in East Falls, behind the Art Museum, and runs for miles along the Schuylkill River. And now the path has been extended down to South Street. (Closed to auto traffic during regattas and the US Pro Championship Cycling Race.)
You can also find equally nice paths along Martin Luther King Jr. Drive (formerly West River Drive), on the other side of the river, plus King Drive is closed to traffic and open to everyone on foot every Saturday and Sunday from 8am to 5pm, April through October.