The Hranice Abyss

The Hranice Abyss is a hole in the wooded slope above the Becva at Teplice nad Becvou, a funnel of limestone with green water lying at the bottom. What you see from the fenced platform is unremarkable: a drop of some seventy metres to a small lake in a shaft. What is under the water is not. Divers and remote probes have followed the flooded shaft down past four hundred metres without reaching a floor, which makes it the deepest known freshwater cave of its kind anywhere. The water is warm and acidic, charged with carbon dioxide rising from deep in the crust, and it was that gas, not rain from above, that ate the shaft out of the rock.

What you actually see

• The viewing platform - the fenced deck on the rim, looking down the funnel to the water surface.
• The green lake - the small pool at the bottom of the dry shaft, the top of a flooded system of unknown depth.
• The forest path - the marked walk up from the spa, with information boards on the diving expeditions.
• The Becva valley - the river gorge below, with the spa buildings and the limestone slopes above them.

When to go

April to October, when the path is dry and the trees are in leaf. Morning light reaches into the funnel better than afternoon shade. It is a short visit, so combine it with the aragonite caves nearby or a walk along the Becva. Ice makes the approach path awkward in winter, though the site stays open.

Honest expectations

The interesting part is invisible: you are looking at a hole with water in it, and the record-breaking depth exists only on a diagram. Trees and the fence limit the view down. The whole stop takes twenty minutes and does not justify a long detour on its own. Diving is for expedition teams only, and there is nothing to do here but look.

Nearby

The Zbrasov aragonite caves, warmed by the same rising gas, are a short walk down the hill.