Every department store in Germany used to have a paternoster, says Patrick Carr of the Elevator History Museum. But that was the late 1960s, and now the idea of a passenger standing by an open elevator shaft and hopping into a box at exactly the right moment sounds risky. Today, these oddly-designed lifts are fading from European cities, and soon travelers might not have a chance to ride them any longer. But what exactly is this scary-sounding contraption?

The paternoster, pictured above, consists of two elevator shafts side-by-side, with no doors. Within them, a chain of compartments—also without doors—moves continuously on an endless belt, like a weirdly efficient Ferris wheel. In one open shaft the compartments go up, and in the other they come back down. If a person stays in their small cabinet after the last floor of a building, they may fear certain death, or think they’ll be turned upside down, but the box they’re standing in just keeps going up or down and around again, like a Ferris wheel, plunging them briefly into darkness until they again reach an open floor.

This odd elevator was once somewhat common. It was invented in the 1860s by Peter Ellis, an architect from Liverpool. Carr has documented well over a hundred paternosters, mostly in Germany, some of which still exist and some of which have likely closed. As of 2006, there were about 70 paternosters in the Czech Republic, according to a Radio Praha segment from that year. A paternoster enthusiast named David Kabele told Radio Praha that many paternosters in England and elsewhere were shut down in the second half of the 20th century because of their perceived danger, but that in Prague they remained, “because the Communist government wasn’t very afraid of European standards and norms.” It wasn’t until the 1990s, Kabele says, that some Czech buildings took their contraptions out of operation. Today, a directive in Europe forbids the construction of new paternosters.