Covão dos Conchos

The Covão dos Conchos is not a natural feature and not a sinkhole, though it has circulated online as both. It is the intake of a tunnel built in 1955 to divert water from the Ribeira das Naves into the Lagoa Comprida reservoir, part of the hydroelectric system on the Serra da Estrela plateau: a bell-mouth spillway of stone with a rim about fifty metres across, standing in a lake, which water pours over from all sides and disappears into a tunnel about a kilometre and a half long. Seen from the bank it looks like a hole swallowing a lake, and photographs of it go around every few years captioned as a natural phenomenon. Reaching it means a walk of about five kilometres each way from the road near Lagoa Comprida, on rough plateau ground at around 1,600 metres with no shade and no shelter.

What you actually see

• The bell mouth - a stone spillway rim about fifty metres across in the lake.
• The 1955 construction - a hydroelectric diversion, not a natural sinkhole.
• The tunnel - a kilometre and a half of bore taking the water to Lagoa Comprida.
• The plateau - rough open ground at around 1,600 metres.

When to go

June to October; snow closes the plateau in winter and the walk is exposed. Three to four hours return. Water pours over the rim most reliably after rain or snowmelt.

Honest expectations

Ten kilometres of walking on rough ground with no shade or shelter, at 1,600 metres. In dry spells the water level drops and the spillway does not flow, which removes the whole effect. It is a piece of hydroelectric engineering, whatever the captions say. Weather on the plateau turns fast.

Nearby

Lagoa Comprida is on the road; Torre and the Zêzere valley are south-east.