VISIT TO LISBON
If you have lived in Spain a certain amount of time (including in Barcelona), visiting Lisbon and Portugal changes from being an option to an obligatory trip. It is close (2 hour flight from Barcelona), the two countries have history, the languages are similar and all of your friends who have already been there are saying you should visit it.
If you decide to visit Lisbon (or when you decide to do it) keep in mind that there are many companies flying to Lisbon from Barcelona, so explore all the options you have. Additionally in the websites that search for offers (like Atrapalo), there are often good offers for 3-4 days stay (completely enough to see Lisbon and the surroundings).
Lisbon is a beautiful city, around 3 times smaller in population compared to Barcelona, so when you are there you can actually relax and feel you are in a quieter place. The city has its own charm with the steep streets , old buildings, great night life and of course the yellow tram. For seeing the city you will need around 2-3 days, even without the need to take a tour bus. Must sees are: Tower of Belem, the neighborhoods Alfama, Baixa, Chiado y Barrio Alto, Jerónimos Monastery, Tram 28, Santa Justa Elevator, Pedro 4th Square, and Castelo de Sao Jorge. And of course don’t miss to try the tasty “pasties de nata”, sold all over the city, but most famously at Pasteis de Belem where a family has had this restaurant for a long time where they bake their own special version of this delicious pastry.
If you are there for more than two days you will definitely have to visit Sintra. It is a small village, located about 40 minutes by train from Rossio train station. Must sees there are the Pena National Palace and Sintra National Palace. Pena National Palace is surrounded by woods, with a wonderful walk back down the hill to the bus stop through beautiful trees and small lakes with white (and black) swans.
Another highly recommended day trip is to Cascais, Cabo de Roca (the most Western tip of Europe), and the amazing beaches and coastal villages that you will find on the way there. The combination of the rocky beaches, the ocean and the incredible nature surrounding the northern coast of Lisbon turn it into a breath-taking place. For this trip it would be easier to rent a car for the day and enjoy yourselves.