Very popular uphill area for hiking, and running, so you'll likely encounter other people while exploring. There is a beautiful view at the top. Get the S2 train to Peu Funicular from here you are at the bottom. If you’re feeling brave, run up from there or there are more funicular and bus options to run around closer to the top.
More information here
Arc de Triomph is a nice, spacious flat area for running. A great starting point to then go to Ciutadella park or the beach.
It's getting hot right? For a nice sea breeze try running along Barceloeta beach up past Bogatell. Paved paths, marinas, and numerous landmarks. More info here.
Fancy a beautiful view? If you want a challenge to run up the stairs there are also great places for calisthenics and yoga. To get here take the metro to the Vallcarca station. More info here.
Centrally located, easily accessible and green. If you're looking for a small and quick space for a run, this 1 mile parameter park is great to see how many circuits you can make. Pass the small lake, fountain and zoo, go for as long as you need and make it home easy. More info here
Although there are some flat bits, prepare for a lot of stairs. Montjuic offers beautiful gardens and one of the best panoramic viewing points of the city. Get the L2 to Parallel and then the funicular up to montjuïc.
One of the largest urban parks in the world. Great views of the city, the Gaudi cathedral, and the Mediterranean, with markers along the way. There are many other trails in the park for running. Very Hilly! Get the S2 Train from Placa de Catalunya to Baixador de Vallvidrera, from there you can get a bus to the top from FGC Baixador Vallvidrera to Lila - Menta, or you can just run there. 4.85 miles one-way.