The old Santa Clara convent, on the west bank of the Mondego opposite the city, was built in the early 14th century for the Poor Clares. It is a remarkable ruin — Gothic arches rising from a partially excavated space that was flooded for centuries after the Mondego repeatedly inundated the site. The convent was eventually abandoned in the 1670s when the nuns moved to a new building on higher ground.
The ruined church has been excavated and stabilised, and you can walk through it with a guided tour or audioguide. The cloister is largely gone, but the nave, the rose window above the portal, and the tomb niches are evocative. The story of Inês de Castro — the murdered lover of Prince Pedro, around whom a great deal of Portuguese romantic mythology has built up — is told in detail at the site.