This old building is the biggest station in Sweden. It opened in 1871 and today is one of the centers of operation of most importane in the north of Europe. It´s interesting to see the day to day life of the Swedes combining the train and the bicycle to go to work.
The metro is divided into seven lines, sorted by different colours. The rocky ground and number of steep slopes in the city made construction of the tunnels difficult. The stops are well-spaced, and it takes about 3-5 minutes to reach your destination from any metro stop in the city centre. Along with the tram and bus, it's run by the SL Company (Storstockholms Lokaltrafik). If you want to use the metro, there are a number of different ticket types on offer. For tourists and visitors, the most common is the single ticket or a multi-day ticket, which if you're staying for a few days, is a good option. The metro has good security, and is very safe - I don't recommend trying to travel without a ticket, as there are always security guards.