Barcelona in particular is an exceptionally pet friendly city. Stroll through the streets and witness the large number of owners walking their dogs, or sitting on benches while letting their pets 'get to know' their neighbors in the park. It's a city where you can pretty much walk anywhere, making it that much easier to own and cater to an animal. And when it comes to hotels, there are plenty of viable options, many of which comes with specific pet-friendly services such as dog walking, grooming and even more specialized care from doggie clothes to high-end accessories (depending on where you're staying).
Most pet friendly hotels have a few regulations, whether it's the number of pets allowed in the hotel or how much weight you’re allowed to bring in with you (petwise) and there is very often a 'pet surcharge' depending on the hotel. If you’re choosing your hotel based on how pet friendly it is, it’s definitely worth looking into how much the surcharge will run you, as some hotels let you bring in pets for free while others charge you by the pet and by the week. Another great thing about the city is that in conjunction with the pet friendly hotels, there are plenty of dog walking services, especially ones that have emerged in recent years. Ask your hotel to connect you with some if you want your dog to have an extra special experience in the city.