Montjuïc is the local mountain of Barcelona. It is prominent located at the seaside and better reachable using public transport than Tibidabo mountain. Additionally you will find a lot of sights and attractions to spend even more than one day. At the top of it the Castell de Montjuïc is situated – an old fort, beeing used to defend the city and the port in old times. Until today there are ruins of enormous guns installed. Many parks and gardens border the lower levels of the fort.
Another stop-over travling downwards Montjuïc would be the Olympic Stadium, which was built for the Olympic Games 1992. We all remember the famous song of Freddy Mercury and Montserrat Caballé which has been performed at the opening. That, by the way, happened a little bit further down at Font Magica (magic fountain) in front of the Palau Nacional, which holds a museum today. At the Font Magica you can see some nice water and light performances every summer weekend in the evening. (Attention: hotspot for pickpockets!)
Metro & Paral-lel, inside the station change to Funicular de Montjuïc. After the Funicular the Bus 193 takes you directly up to the Castell.
Metro & Placa Espanya. short walk direction Montjuïc.