There is a nice place for a swim in the river in the northwest corner of Mansilla. Cross over the small pedestrian bridge towards the camping place (not the road bridge that the camino crosses) located in the northwest corner of town. Getting there will take you through several of Mansilla’s small plazas.
Mansilla still has large sections of its defensive walls, turn back when leaving town to get the best view of them. Much of the way between here and Puente de Villarente is adjacent to the road.
Mansilla traces its history back to Roman times, and the walls that continue to surround most of the city bear evidence to its importance; it was both a layover on the Roman road to León and a market town (mostly mules).