The climb begins at the camping area of Selva de Oza, on the upper valley of the Aragón Subordán. To get there, start from Huesca or Pamplona, in northern Spain. From any one of both towns, follow road N-240 towards the other one. At Puente la Reina (88 km away from Pamplona, or 72 km away from Huesca) you will have to turn north by road A176. This is the road running alongside the river Aragón Subordán, entering the Valley of Hecho. Follow the A176 up to the village of Hecho. After crossing Hecho the road becomes sensibly worst, but goes on to the Boca del Infierno (that's a narrow pass) and Selva de Oza (see approach for Castillo de Acher). Leave your car at the camping area of Selva de Oza.
The general line of the climb follows a steep scree slope from the camping area of Selva de Oza, in search of the Collado de Arriba de Lenito. After that it turns right to meet a final ridge and calls for a minimal scrambling ability.
Start walking at the camping area, taking a wide westwards track that climbs the Barranco de Estriviella. It's clearly signmarked by a wooden signal ("Sendero a Estriviella y Peña Forca"). After about one hour, the track turns into a small path but keeps going west and soon overcomes a rocky step. You will enter a wide grassy area closed (in front of your position) by the east face of Rincón de Alano. After walking west for some five to ten minutes, turn left (grossly south-southwest) to overcome another rocky step through a grassy slope. This path might prove a little bit difficult to find at first, but cross the river and head for the grassy slope southwest of your position. After crossing this second step you will be facing the long scree slope leading towards Collado de Arriba de Lenito. All that is left will be a matter of walking up the scree, through some sections of bigger rocky blocks, for about an hour up to the col. Up there you will turn right tof face a grassy slope leading in about thirty minutes to the eastern summit of Peña Forca. Be careful in this last grassy slope, it can be dangerous if you find it covered by snow.