Entrance to the cathedral is free (which is unusual, so the feeling of unexcitement about the interior is likely universal), but 10 euros gets you entrance to the museum, the bell tower and the dome, both of which you can climb up. It isn’t quite as exciting as in Assassin’s Creed II, but you also don’t need to have the super-human climbing and jumping skills that the game requires. (Jumping up and backwards three feet and catching on to a ledge? Yeah, right.) The lines are about an hour long for each, but definitely worth it.