The Castro Marim and Vila Real de Santo António Marsh Natural Reserve covers the Guadiana estuary north of the city — a mosaic of salt pans, mudflats, and reed beds that is one of the best birdwatching sites in southern Portugal. Greater flamingos are present year-round and are often visible in large flocks from the road. Spoonbills, avocets, black-winged stilts, and dozens of wader species pass through on migration.
The reserve entrance is a few kilometres north of Vila Real, just off the N122. There is a visitor centre at Castro Marim and a network of walking paths through the salt pans. The salt production here is among the most traditional in Portugal — look for the characteristic wooden tools and shallow evaporation channels. The medieval Castle of Castro Marim sits on the hill above the reserve and makes a natural combined visit.