It's maybe the most heavily planned and designed European capital.
Maybe it's hard to see that coming from the US where all the cities have been planned in the last centuries and you are used to see blocks everywhere, but in Europe it's the exception, and the way it have been done in Barcelona is, I think, unique in the world.
If you don't know the concept of superblocks, there you go : https://www.citiesforum.org/news/superblock-superilla-barcel... but to summarize, Barcelona have been divided in superblocks containing blocks. Inside those superblocks, there are less cars and inside the blocks, there are barely any car at all. What that means is that each superblock is like a little city and each block is like a peaceful village. Hundreds of peaceful places inside of a busy european capital.