That is a ticket you get in a museum when you leave your coat in the cloakroom.
I think I didn’t mention a really funny story. Back in Vienna we went to Albertina with my friend and we had to put our coats in the cloakroom where we were given our tickets which I wisely put in the back pocket of my skirt. When we finished our tour in the museum we went to collect the coats and… IT WASN’T IN MY POCKET!!! I checked it a few times and my bag and the other pockets and again and again and I lost it. I was gutted. Luckily we managed to explain it to the lady in the cloakroom I lost the ticket, I described my items and she kindly gave them to me. I kept checking it for the rest of the day and I still haven’t found it. Up until the point we got home in the evening and as I put my hand in my pocket IT WAS THERE!!!!
I don’t know how it could have happened. I checked it! I swear!