Hard to choose the best viewpoint in Lisbon, but São Pedro de Alcantara is definitely one of the top ones. It's like sitting on a terrace with a view of the eastern side of the city. There is a kiosk where you can get some refreshments.
7/28/20 Great town. Would like to have stayed multiple nights and explore more. Stayed at Bowen Motel-perfect location. Makes me want to bring a bike and pedal my way around the roads.
I guess it depends on how much of an Obama fan you are! I am a fan, but I would only recommend going if it is directly on your route. We might have enjoyed it more if we had gone when the pub (yes, I think there is only one) was open.