The Schiessentümpel is a waterfall of a few metres on the Black Ernz, in the Mullerthal of Luxembourg, where the stream splits into three arms around one boulder. The reason people come is the bridge over it. It is a sandstone arch of 1879, short enough to cross in ten paces, railed with bare tree branches and with ferns growing straight out of its mortar. It carries no road and never has. One stonemason from a village nearby built it between March and July that year, out of local sandstone and lime mortar. He built it for the visitors the romantic-era press had begun sending into the valley. From the deck you look down onto the three cascades and hear them working under your feet. The way in is a stair of mossy sandstone blocks set into the hillside, dropping through ivy and beech until the traffic noise is gone.
The rock is what made the region. Luxembourg sandstone does not shed rain, it swallows it. The rock holds water in its pores and lets it out again slowly through springs, which is how the Black Ernz keeps running through dry summers. Where the porous slab rests on watertight marl, whole blocks slide apart on it, and that is how the fissures and caves of the Mullerthal opened. Past the bridge you are on the 112-kilometre Mullerthal Trail, and the crowd thins within minutes, because most people photograph the falls and turn straight back. East of the water the path runs into the Kuelscheier, a rock corridor about a hundred metres long, narrow and almost pitch black, its walls pitted with honeycomb hollows and in places close enough to touch both at once. There is a marked detour for anyone who would rather not. One last thing about the arch: the boundary between Waldbillig and Consdorf runs down the middle of the stream, so you change commune halfway across it, directly above the middle cascade.