Museum Old Synagogue in Krakow

You're standing on Szeroka Street, in the middle of Kazimierz, the old Jewish quarter of Kraków. The sturdy building in front of you is the Old Synagogue, the oldest synagogue still standing in Poland. Take a good look at the walls. They're thick masonry, propped up by heavy buttresses. The windows sit high above the ground, and along the top runs a wall with loopholes. It looks more like a fortress than a house of prayer, and that's exactly the idea. This is a fortress synagogue, built to hold out under siege. Very few of them survive.