East of Cordoba and northeast of Cazorla in the Jaen Province, the 2,143 sq.km Parque Natural Sierras De Cazorla has numerous hiking routes through pine forests and over rugged mountain peaks. This is a very popular national park that has over 600,000 visitors annually. Luckily, most of the trails are desolate and you can possibly see wild boar or ibex.
The most popular hike in Parque Natural Sierras De Cazorla is the trek along Rio Borosa. The route along Rio Borosa is a 24km round-trip trek taking about 8 hours. The route climbs along the river and passes through a narrow 1.5km section known as Cerrada De Elias gorge. Beyond the gorge, the route climbs more and eventually passes through two short tunnels. Above, you will reach a reservoir Laguna de Aquas Negras and eventually a natural lake, Laguna de Valdeazores.
To reach the hiking trailhead for Rio Borosa from the town of Cazorla, head northeast on A319 for about 20km. At Centro de Interpretacion Torre del Vinagre, veer right on Central Electrica access road crossing Rio Guadalquivir. At 1.5km, park near the fish farm. The marked trailhead is just past the fish farm on the right.
The town of Segura de la Sierra makes a great scenic base village -- check out the castle and the muslim baths.
Overall, Rio Borosa Trail is the 7th most popular hiking trail of all 21 hikes in Spain.