Opening the underground door into a wall of darkness, the museum feels a bit like being in an Indiana Jones film. The flickering lamp light shows sand, rubble and a narrow staircase before you reach an ancient window with a curving arch, located 14 metres below ground level. It looks like the tower of a castle, with stairs leading down the wall and a glimmer of black water below. This is the mikvah, the ritual bath of Cologne’s medieval Jewish community. The museum, located close to Cologne’s famous cathedral, is unlike any other. Called MiQua in reference to the mikvah, it will feature a 600-…