I was dumb. Don't be me.
I'm from the US and live in a state where recreational use is legal. My 2nd day in Barcelona I went to a club and purchased a membership and a few pre-rolls. The following day we had our much anticipated tour of La Sagrada Familia. I wasn't thinking. I put my purse through the x-ray and security flipped out when they realized I had weed. They said it's illegal, I said but I just purchased it from a club....? I was refused admission. I tried to come back through the line a few minutes later without it, but the same security guard saw us and refused to let us in. They said "not today"...but I didn't want to mess with trying to buy more tickets or being refused for showing up on the wrong day...so I guess this means I'll be back someday. Barcelona was wonderful.