Sintra is a perfect day trip from Lisbon. There is plenty enough to do and see to fill an entire day and then some. Among many of its amazing sights are the National Palace in town, the whimsical Pena Palace atop a huge hill, the romntic Quinta da Regaleira, and the oldest castle in Portugal, the Moorish Castle (pictured here). We somehow managed to cover all 4 of those sights in a day (and return to Lisbon exhausted). It's not the best place to go if you're afraid of heights or don't want to climb a lot of steps, but the views from this fortress make it worth the climb.