The Legazpi district in southern Madrid’s has a great park system surrounding the Planetarium. Paths in the Parque Tierno Galván begin along the railroad tracks near Calle Parroco Eusebio Cuenca, then continue around the park for about 3 miles (5k). There are some opportunities for fun stair climbs, and fantastic views from the hillside.
Longer Run: Just south Parue Galván (and a bit of a highway tangle), the Manzanares Lineal Park is has some lovely paths for running. Just west of there, there are two decent-sized parks in the Usera District: Parque de Pradolongo features a lake and jogging paths and Parque Emperatriz María de Austria features wooded paths, meadows, and some sports facilities. A loop of those two parks combined is ~ 5 km.