The Kuelscheier, a torchlit squeeze through the Mullerthal sandstone

If you’ve never done anything underground and fancy a small, safe dose of adventure, this is the place for it. The Kuelscheier is a cluster of sandstone rocks just outside Consdorf with a cleft about 100 m long running right through. Unlike the other clefts in the Mullerthal, it’s roofed over, which turns it into a proper tunnel with no daylight at all. You walk through by torchlight, and in the tightest bits only one person fits.

How the rocks split

visitluxembourg explains the geology. The tunnel opened up when big blocks of sandstone separated along cracks in the rock face. A spring rises beneath the rocks, right where the porous sandstone meets the less permeable clay marl underneath.

The name is a nice bit of local history. Kuelscheier translates roughly as charcoal barn, and the most likely story, according to the same listing, is that coal from the area was stored for a time in the clefts, which acted as a shed. The family discovery tour on visitluxembourg turns this into a children’s story in which the kids come out with black faces.

Torch, head torch, or phone?

A torch at the very least. The Mullerthal Trail website calls the passage very narrow and completely dark and strongly advises bringing one, and visitluxembourg lists it as necessary. I’d go for a head torch, since in places you’re feeling your way along the rock with your hands, and keep the phone in a pocket.

The other thing to know is that some sections are so narrow the listing talks about one-way traffic. Hear voices coming towards you and one party has to wait or reverse, so on a sunny Sunday I’d expect a bit of queuing.

If you are staying the night, see the best hotel deals in Berdorf for your dates: the well-placed rooms go fast.

Where the trail goes

Route 2 of the Mullerthal Trail, the rocks loop, passes right through the Kuelscheier, coming from Müllerthal past the Konsdref mills and carries on towards Scheidgen. If the tunnel is too much, the trail website says you can easily walk round the outside. That’s not true of the Rittergang and the Déiwepëtz, two narrow passages close by, which have no way round.

For the tunnel on its own, local path C2 is a 4.2 km loop. The family version described by visitluxembourg starts at Op der Gare, beside a Second World War aircraft that crashed nearby, drops along a narrow path into the valley of the Härdbaach stream, detours through the Rittergang and the Déiwepëtz and finishes with the Kuelscheier.

Bringing children

From about age six, I can’t think of much in Luxembourg they’ll enjoy more. If you’d like a guide, the Mullerthal tourist office runs Adventure Kuelscheier, a 3-hour children’s hike in English, German, French, Dutch or Luxembourgish, at €145 for a group of up to 15. Going it alone, path C2 and one torch per child is enough. Consdorf also has the Joffer Margot nature trail, 8 km with a short-cut that brings it down to 4.6 km. There are more family ideas in Luxembourg with kids.

For a change from rock and darkness, the Kallektuffquell, a moss-covered tufa spring in the Black Ernz valley, is on Route 3 in the same commune.

If you are staying the night, see the best hotel deals in Berdorf for your dates: the well-placed rooms go fast.

So you do not lose the morning at the ticket office, browse tickets and tours in Kuelscheier on GetYourGuide.

If you would rather go at your own pace, see the car hire deals in Luxembourg: the earlier you book, the more cars are left to choose from.

Before you fix your dates, compare tickets to Luxembourg: the same journey can cost very different amounts from one day to the next.