1. Don’t underestimate the pickpockets and rip-off artists here in Barcelona. It is the number one pickpocketing capital of Europe and one of the top pickpocketing locations in the world.
2. You will be surprised by the insane line to see the famous The Sagrada Familia, it could literally be miles or kilometers long. So if you want to go see it go early in the morning or book your tickets ahead of time to skip the line.
3. Spanish culture is very relaxed and the same applies to time, when in some countries the restaurant will open exactly at 6 pm or a train will depart at exactly what its mentioned in your ticket, that’s not necessarily the case here.
4. Watch what you wear there! In Barcelona, it is illegal for men to walk around bare-chested or for a woman to only wearing a bikini top, except at Barcelona’s beaches and on the streets very close to the beach. So in addition to this, if a woman is wearing what is deemed as a revealing outfit or very short skirts, they might not be allowed to visit the Barcelona Cathedral. So it's better to dress in the safe side.
5. Driving in Barcelona is dangerous with an accident occurring in the city every 19 seconds.