There's a station of the subway right at the airport (Aeroporto).
You will catch the E line (Aeroporto - Estádio do Dragão). At the metro station there is a machine, where you can buy your ticket (the ticket is called Andante).
You have to buy one Andante per person!
In the machine, you can change it to english, you choose "buy", then you have to pick the Z4 journey, and buy as many journeys as you want (since everything is near the apartment, you can buy just one at first).
You can buy as many travels as you like on your Andante.
Each travel allows you to travel within 1 hour through different stations.
Everytime you enter the metro, you have to validate your Andante before (there's a yellow detector in the station, you just have to pass the Andante there).
You will be out on the Bolhão station. Which is 1 minute walking from our apartment, so it's really nearby.
The adress is: Rua de Santa Catarina, number 450, 3rd floor . It's a green door, next to a waffle shop.
