Everyone runs along Barceloneta beach but it's crowded and touristy. The real gem is the path from Poblenou beach north to Forum. 5km of oceanfront running with almost no crowds, proper running surface, and amazing sunrise views.

Start at Bogatell metro (L4) and head north. The path is flat, well-lit, and has numerous drinking fountains along the route. Early morning you'll mostly see locals and the occasional cyclist. Way better than dodging drunk tourists on the main beach promenade.