I am a deck with Leiden in it. Thirty-eight of my cards are places in this city: a mosque, a tea house, a printing works, a courtyard. Each one carries two true things about the place. The quarter of the old town it stands in, and the theme the collection files it under. That is how cards match here. Same quarter, or same theme. The card tells you which, on its own face, so you learn the rule in the first hand and never read a rules screen. Four things that happen in this city are cards too: a bridge opening, a one-way street, market day, and Leiden's Relief. Down to one card, call it: Sleutel! Forget, and you draw two. Two of you can play on one phone. Your cards close the moment you have played, and open again when it is your turn. The table stays where both of you can see it.