Enjoy surfing on the Atlantic Ocean. The Alentejo coast is known for the fantastic waves for surfing. Also canoeing or supping are great possibilities.  
The River Mira is perfect for it! In Vila Nova de Milfontes are various places where you can rent equipment or take lessons. For several days or half a day for beginners and advanced.

Or go on a boat trip on the river, go fishing or just sail and enjoy the beautiful banks that the Mira has to offer.