The forbidding Castell (castle or fort) de Montjuïc dominates the southeastern heights of Montjuïc and enjoys commanding views over the Mediterranean. It dates, in its present form, from the late 17th and 18th centuries. For most of its dark history, it has been used to watch over the city and as a political prison and killing ground.

Anarchists were executed here around the end of the 19th century, fascists during the civil war and Republicans after it – most notoriously Lluís Companys in 1940. The castle is surrounded by a network of ditches and walls (from which its strategic position over the city and port become clear).

Until 2009 the castle was home to a somewhat fusty old military museum, closed since the Ministry of Defence handed the fortress over to the city after protracted negotiations. The artillery that once stood in the central courtyard has been removed, but some of the seaward big guns remain in place.

In the coming years, it is planned to establish an international peace centre in the castle, as well as a display on its history. There will also be an interpretation centre dedicated to Montjuïc. While waiting for this to happen, a modest temporary exhibition has been established in one of the castle’s bastions, on the right as soon as you enter. Called Barcelona Té Castell (Barcelona Has a Castle), it explains something of the history of the place as well as detailing plans for its future. Perhaps when all this is done, the tombstones (some dating to the 11th century) from the one-time Jewish cemetery on Montjuïc will get a more imaginative exhibition space than the drab room once set aside for them in the military museum.

The views from the castle and the surrounding area looking over the sea, port and city below are the best part of making the trip up.

Catalan and Spanish speakers can join free guided tours of the castle on Saturdays and Sundays (11.30am in Catalan, 1pm in Spanish). Group tours (€65 to €80) can also be booked (also in English and French).

Around the seaward foot of the castle is an airy walking track, the Camí del Mar, which offers breezy views of city and sea. Towards the foot of this part of Montjuïc, above the thundering traffic of the main road to Tarragona, the Jardins de Mossèn Costa i Llobera have a good collection of tropical and desert plants – including a veritable forest of cacti. Near the Estació Parc Montjuïc funicular/Telefèric station are the ornamental Jardins de Mossèn Cinto de Verdaguer. These sloping, verdant gardens are home to various kinds of bulbs and aquatic plants. Many of the former (some 80,000) have to be replanted each year. They include tulips, narcissus, crocus, varieties of dahlia and more. The aquatic plants include lotus and water lilies.

From the Jardins del Mirador, opposite the Mirador Transbordador Aeri (Telefèric) station, you have fine views over the port of Barcelona. A little further downhill, the Jardins de Joan Brossa are charming, landscaped gardens on the site of a former amusement park near Plaça de la Sardana. These gardens contain many Mediterranean species, from cypresses to pines and a few palms. There are swings and things, thematic walking trails and some good city views.