Montjuïc Fortress or Castell de Montjuïc stands on the Montjuic castle and has a historical value. Also the castle is very impressive and panoramic views open from the top so you should come there.
The fortress was built in 1640, during the Catalan rebellion against the official Spanish government in the face of the Austrian Habsburgs. 100 years later the fortress was captured by the British, then Spaniards attacked it again, and then in 1808 French troops and Napoleon came here. In 1940 the President of Catalonia, Luis Companys, was shot by the order of Franco, and then for years the fort was used as a prison.
Today people come here to enjoy the amazing Barcelona panorama and the sea views.
You may climb the mountain on foot. It may become a nice walk in spring or autumn but in summer it may be very hot and exhausting. Do not forget about comfortable shoes, water and follow the signs.
The second option is bus 55. Bus number 55 leaves from Pl. Urquinaona and costs about 2 euros.
The third option and the most interesting one is the cable car. During the ride you will see the central part of the city panorama: the Rambla, Placa de Catalunya, the Sagrada Familia Cathedral, the Gothic Quarter, and also the endless sea, golden beaches and the port with its beautiful yachts and liners. There are several places where you can take the cable car: the San Sebastia tower on Barceloneta beach (Torre de San Sebastia), Jaume I tower in the city port (Torre de Jaume I) and Montjuic Park (Parc Montjuic).
In January and February, the cable car is open from 10.00 to 18.00.
In March, April and May, the cable car is open from 10.00 to 19.00.
From June to September, the cable car is open from 10.00 to 21.00.
In October, the cable car is open from 10.00 to 19.00.
In November and December the cable car is open from 10.00 to 18.00.
A round trip ticket costs from 13.50 euros. You can buy a ticket at the cable car box office or online if you do not want to stand in line. The ticket collector will scan the ticket from your phone, you don't even need to print it.
With this online ticket, you can enter and exit at any of these three stations: Parc de Montjuïc, Miramar, and Castell de Montjuïc.