About 1 kilometre out of Castrojeriz the track joins a restored section of roman road originally built to provide a solid route across the boggy Odrilla valley. Soon you will come across a wooden footbridge across the Rio Odrilla and then the steep climb up to the Alto de Mostelares.

LL: cross the Río Odra via the Puente Largo de Bárcena, a medieval stone bridge—low, narrow, and long—with several arches.
Nowadays, the bridge is almost invisible to those crossing it: it has no side parapets, the surface is dirt