Head down river by canoe. Pause to admire the green of the river banks and the fish and animals accompanying your descent. Match improving your canoeing skills with the beauty of nature.
Spend a morning in the saddle, cycling the surroundings of wherever you are staying. Alternatively, stay in the hotel and ask around to find somebody to join you for a couple of games of tennis.
If hunting and fishing is your thing, the Trás-os-Montes rivers and countryside provide for excellent conditions. Spend a very different kind of day tracking down wild boar. There is also good trout fishing, partridge and hare hunting catering both for the beginner and the more proficient.