Last summer I went to Lisbon and I had a great time there. I highly recommend it to you!! Taking a stroll through the Chiado area is a must. You can also visit the Sao Jorge Castle, or go to the Miradouro de Nostra Senhora do Monte, from there you will get an excellent view of the city.
Hop on and off the trams, have a coffee while you see the tourists and locals passing by, get lost in any of the quiet streets, there are lots of things to do!
Sintra and Cascais are the villages I visited that best keep the Portuguese flavour. Don´t forget to taste their cheese and cream cakes. You won´t regret it!!