Lisbon is known as the city of seven hills, and for that reason often compared to San Francisco. They also have trams and the iconic Golden Gate-esque, Vasco de Gama Bridge. At the top of one of these large hills, just above the charming neighborhood of Alfama, the Castelo do Sao Jorge offers outstanding views of the city and Tagus River.
St. George's Castle is at least as old as the 8th century BC, or in other words, very old. It has 11 towers in total: a few closed and a few we opted against climbing for the sake of our knees. But all told, you get 360-degree views from these towers, and they are easily the best views of Lisbon. The castle grounds are also home to an absolute ton of peacocks just hanging about, so that was cool.
There is an archeological site, and the castle was very cool. Even without this, honestly, it was worth it for the views alone. Definitely worth the trek to get up there!