I checked my Airmap app and it shows Barcelona as custom.
So I did some Googling and found this article from December 2017 that states that ALL of Barcelona and the mountains behind the city are forbidden to drone flights.
It also states that the Spanish government will and has fined violators.
@Spark 317 Thanks for the comprehensive answer. Now it's clear why the whole Spain is colored yellow on Airmap.
Haven't seen any drones by myself in comparison with lots of uncontrolled flights in Moscow/St. Petersburg (Russia). However, I saw some really nice drone footages of Barcelona.