Vila Real de Santo António (normally shortened to just Vila Real) is the main border town between Spain and the South-East of Portugal. The closeness of Ayamonte in Spain (just a few minutes ferry journey across the Guadiana River - there is also a bridge) used to be seen in the way that shops showed their prices in both currencies.
Apart from travelling across the river to Spain (do remember that if you have hired a car it will almost certainly not be insured to cross into Spain) the only major item of interest to the tourist is the main square. This, cardinally arranged, tiled square tries to emulate that of Seville but while it is worth a look it does not have Seville's ambience or style.
To the north (about 3km) is Castro Marim. This boasts a spectacular Fort which is well worth a visit. In terms of history, it has features from every period since around 700 AD. The view from its battlements encompasses Ayamonte in Spain and south (back towards Vila Real) looks out across a nature reserve of international repute for migrating birds.
See also the nearby area of Monte Gordo.