The Ajuda National Palace is in a remote area of central Lisbon, so you have to take a bus/tram to get there. Admission is € 5, but with a student card it's free, on Sunday morning it's also free. The palace is beautiful, both outside and inside, with some furniture, ceilings, lamps - precious. I loved it. To complete the look, you can see the Ajuda Botanical Garden, which is right across the street from behind the palace.