Take a day out to explore Montjuïc Hill, the broad flat mountain that rises as a sheer cliff from the harbor. The fastest and easiest way to get up there is the Montjuïc funicular that connects with the Metro at Paral-lel Station, Lines 2 & 3, which takes just two minutes and is included in your regular ticket. A cable car goes on up to Montjuïc Castle where Bus #150 also stops. There's also a 10-minute cable car ride from Barceloneta Beach with a great view of the seaport.
Once up there, it's up to you to decide how to spend your day. You won't be able to see it all. Montjuïc Hill, a favorite destination for amateur cyclists, is where many of the 1992 Olympics events took place and a number of cultural attractions are located. Check out the Olympic and Sports Museum for an overview. Nearby the old botanical gardens is a good place to stroll and is free on Sundays after 3 pm. Feeling more active? Try rock-climbing at Climbat, the largest "rocòdrom" in Europe. The Montjuïc Park is a pleasant spot for a picnic or a stroll or a visit to the Fundació Joan Miró.
The Ten's tapa restaurant in the Park opens at 8 if you're ready to call it a day or the bars, restaurants and clubs of Gaixemplo are only a five-minute Metro ride away.