There is a splendid aire in Coimbra located conveniently beside the river and close enough to the old town to be able to visit on foot. There were 40 or 50 vehicles when we were there. There is fresh water, and toilet disposal but no toilets or showers.
Coimbra also has free wifi - not available from the aire but cross the pedestrian bridge and you find it there.

University of Coimbra

We came to Coimbra to visit the university which was first established here in 1270 and to see the famous Biblioteca Joanina - the baroque library. To visit the library you need to book, there are 20 minute slots and no photographs which is a pity as it is a gloriously over the top piece of baroque decoration. Beside the library though there are other buildings to visit at the university and you can take photos. Be warned though the university is a strenous walk up a steep hill. Students  in full three piece formal suit may accost you to sell you post cards and guidebooks -  you feel pretty sorry for them on a hot day having to wear heavy dark clothes.

Riverside walk takes you to bridge to aire