West of Madrid and south of Avila, the Sierra de Gredos is known for its lakes and granite mountains. There are numerous mountain bike trails to shread.
The best time of year for exploring the Sierra de Gredos is March to May and September to November.
Note: there is limited bus access to the Sierra de Gredos, so a car is desirable. The town of Arenas de San Pedro makes for a efficient base to explore Sierra de Gredos.
Overall, Sierra de Gredos is the 20th most popular mountain bike trail of all 20 mountain biking rides in Spain.