At the foot of the Sierra de Leire, a huge green and blue stain spreads for 10 kilometres, even further beautifying a landscape dominated by Portuguese oaks, beech and pine woods which herald the proximity of the Pyrenees.  The dam, further upriver close to the town of Yesa, is 400 metres long and 75 metres high. In Yesa you can visit the remains of the Roncaleses bridge over the river Aragon, which was built at the end of the 11th century. Near the reservoir you can visit Sangüesa, a monumental city crossed by the Pilgrim’s Way to Santiago, or the Castle of Javier where the patron saint of Navarre, St Francis Xavier, was born. If you like the idea of listening to Gregorian chant in a medieval building perched at the top of a mountain, make sure you visit the Monastery of Leire