Tickets for The Last Supper in Milan must be bought in advance as Leonardo da Vinci’s famous painting on a wall in the refectory of the Convent of Santa Maria delle Grazie in Milan may only be seen with reserved tickets.
From WIkipedia: https://en.wikipedia.org/wiki/The_Last_Supper_(Leonardo_da_Vinci)#/media/File:%C3%9Altima_Cena_-_Da_Vinci_5.jpg
