Drone footage reveals the spillway in the middle of a tranquil Portuguese lake

While it may look like a natural phenomenon, this watery sinkhole is anything but. Named Covão do Conchos it is regarded as one of Portugal's top secret attractions. The mesmerising whirlpool, which has been caught in high definition by a circling drone, is the work of human engineering and can be found in an otherwise tranquil lake in Serra da Estrela Natural Park. People say the opening in Portugal's largest protected area looks like it's from an otherworldly dimension. However, it is far less mystical and far more fascinating.