Ilha do Tavira is one option - there's a very reasonably priced ferry goes from the riverside.
We headed to Faro Old Town on the train from Tavira in March this year.
Looked around the Old Town, GF went into the cathedral, visited a gallery or two and had a very leisurely lunch and walked back to railway station. Everything in 4.5 hours.
Can get train from Tavira to Villa Real do Santa Antonio, walk into town centre, have a look around and a coffee and then get the ferry across the river to Ayamonte to have lunch in Spain.
Time travel too on the way back because of the one hour difference between Spain and Portugal. We left Spain at 15.00 and arrived in Portugal at 14.20...
We were staying in the Pousada in Tavira in March this year as a result of getting a good over-55's deal on the hotel, but the places we ate in included family run restaurants such as Bica, Casa Simao and Churrasqueira O Manel, all across the river from the main part of the town.
One thing that we did notice was that several people who were also staying in the Pousada were eating out in town and at the places we were frequenting rather than using the hotel dining room.
All of the above mentioned were quite busy, usually with locals, family groups and a few fellow Brits who were going for the local cuisine.
Self and partner ate well on each night out with the highest bill being €40 for our meal on the last night - two main courses, two desserts, coffee plus a bottle of wine and a bottle of mineral water too.
Other top tips for Tavira is that there is a Lidl next door to the railway station so you can stock up on bottles of mineral water etc and put them in any minibar fridge too (we made sure that we bought a different brand to that which was already in the fridge).
Tavirense near the cinema and the cafe on the end of Praca da Republica are places to go for good coffee and cake.
Worth ensuring that you have some small change with you at all times to pay for coffee or other small purchases. We didn't have any problems in Tavira, but on our other visits to Portugal over the last year, changing even a €5 note was a challenge in some cafes or mini-markets, especially if the till user doesn't speak English and you don't speak Portuguese!
Hope that this helps in some way...
