From Puerto de Cotos walk up the dirt track heading north. The track makes a sharp left turn after Fuente de Cubeiro (water source). Follow the footpath right behind the shelter. It will take you first across the forest and then across the bushy south-eastern slopes of Dos Hermanas, all the way to the stream draining the Laguna Grande. Cross the wooden bridge and climb the Circo de Peñalara eastern moraine. The path starts a short descent after a massive cairn. 10 ' more will take you to the Laguna de los Pajaros, right below Peñalara's south-eastern face. Count on 1 h 30' from the parking at Cotos
The first part of the route follows the evident corridor to the left of the 'Pared Negra' (black wall). Although it narrows at points to just a couple of meters, it 's never steeper than 40º. Once above the 'Pared Negra' there's a wide platform from which there're several alternatives. The direct climb to the summit is the most difficult (mauve trace), up to 50º (perhaps AD-??) along a bending corridor.
The most evident route climbs straight to the breach between Peñalara and Risco de Claveles (pink trace). The last few meters before the ridge are about 45º, although it's possible to avoid them making right turn. The ridge to the summit is wide and flat, 2' walk up. All in all, it's about 300 m in heigth, 500 meters long. In good conditions, the climb takes little over half an hour.
Between December and April, even May (2002, 2003), crampons and an ice-axe are a must. With icy conditions you won't regret bringing a rope and a 2nd ice-axe for the variant on the left.
I've done the descent on short figgle skis as late as May 10th... bring your helmet!
With snow, this is to me the most elegant not-so-technical way of reaching Peñalara... as far from the maddening crowd as you can be on this mountain.