There are currently no laws against nudity in public in Spain, which means that you can go anywhere in the country naked. However, whether this means the residents of Spain would be happy for you to walk in the nude down Las Ramblas is questionable.
Nudism is only really practiced on Spain's nude beaches, which are mainly in Catalunya, especially around Sitges where you can find Mar Bella, Playa de las Balmain, and Playa Muerto. There are also a number of great nudist destinations in Spain, but just because the law allows for nudism in public doesn't mean you should go everywhere without your clothes.
Knowing when it's appropriate to go clothing-free comes down to understanding the Spanish culture as it relates to being naked. While Spaniards don't find women's breasts taboo like Americans, going fully naked it still considered inappropriate it most public settings.
The Culture of Nudity in Spain
While toplessness isn't really considered taboo in Spain as a whole, some parts of the country are a bit more reserved when it comes to full nudity. Barcelona and other major metropolitan cities have a much friendlier view of naturism and toplessness than some rural coastal towns.
The local government in Cadiz, Andalusia, for instance, has raised the possibility of fining people caught naked on their beaches, and many family beaches around the country would frown upon going naked. Restaurants, bars, shops, and business also generally refuse service to people without clothing, so you won't be able to travel everywhere naked.
Still, Spanish culture is pretty open when it comes to sexuality, and toplessness is pretty much universally accepted on beaches in Spain. If you're in doubt of whether or not nudity is acceptable where you are during your trip, just look to the locals and see what they're doing.
Although nudism is perfectly legal in Spain, Spaniards and tourists who are naturists still choose to gather at special beaches and nudist resorts in the country instead.
Among the top nudist resorts and beaches in Spain are Costa Natura in Estepona, Costa del Sol; Barinatxe Nude Beach in Sopelana, Basque County; Playa del Hombre Muerto (Dead Man's Beach) in Stiges; and the Alicante Nudists Bed and Breakfast. At any of these destinations, you won't have to worry about whether or not being nude is offensive—it's encouraged!
Additionally, many of Spain's beaches are nude-friendly, so no matter where you go in the country, there's a chance you can take your tops (and bottoms) off without fear. However, you should always check on what everyone else is doing before you disrobe; if no one else is topless, you should keep your top on or risk offending a family nearby.