Lisbon, the Gates to Atlantic Ocean
Lisbon is a fantastic city. There aren't a lot of sightseeing, but the ones they have are amazing. I would said, that lisbon is a good city to just get lost around. Going up and down on the hills, looking for good views, and also good food. You gonna love the "Pastel de Nata", the most traditional sweet in Portugal. Also, you should taste their see foods, and fish. Really good dishes. So, walk and discover Lisbon on your time.
Insider Tip:If you have time, you should go to Sintra, a old city, nearby, full of mansions and palaces. Amazing views!