Castelo de São Jorge de Lisbo
Why You'll Love It
Castelo de São Jorge dates back to the 11th century and the Moors (it was then captured in the 12th century by the first king of Portugal), but the site has evidence of settlements going back to the 7th century BCE (you can see some of the archeological digs). The palace dates to the 15th century through to the earthquake of 1755, when most of it was destroyed. You can wander the ruins.
Know Before You Go
Super touristy, but incredible views of the city.