West of Madrid and south of Avila, the Sierra de Gredos is known for its lakes and granite mountains. There are plenty of hiking trails to explore.
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 15th most popular hiking trail of all 21 hikes in Spain.