Barcelona is a city with an incredible number of outdoor activities and excursions. From the mountains to the sea, to the parks and wide open areas within the city, you can spend your entire stay outside if that's what you'd prefer (and assuming the weather cooperates which is usually does). No matter what time of year, it's possible to participate in at least a few outdoor activities. Barcelona's seaside boardwalk is a great place to exercise if you want to run, roller blade or power walk. Montjuic is also a fantastic area to stroll through, visit the gardens and have a picnic. You can enter the museums if you want, but if you'd prefer to stay in the sun, this huge 'Mountain of the Jews' provides for a full day of fresh air. If you're more of the park type and want to inject a touch of architecture into the experience as well, Park Guell is a great place to experience Gaudi's magnificent works while enjoying time outside. This huge 'Alice in Wonderland esque' park if a mix of gorgeous and innovative designs intertwined amongst nature. So you can read, have a picnic on the grass and learn about Gaudi's life and his avant-garde imagination.