Charybdis was a sea monster made famous in Homer's "The Odyssey," a creature that swallowed ships by forming a whirlpool. Though merely a myth, if the legend of Charybdis survived today it would probably find itself here at Portugal's majestic Covão do Conchos.

This mesmerizing hole in the middle of the ribeira das Naves appears like a drain, sucking water into another dimension. If not mistaken for a sea monster, it might be taken for a gateway to some sort of magical underworld.

It looks unreal, but it's actually part of a hydroelectric dam system. Built in 1955, the void funnels water from ribeira das Naves to Lagoa Comprida. The mossy growth around the mouth of the 1,519-meter-long hole gives it a natural appearance, despite toying with your intuition in an unnatural way. Perhaps that's part of its enchantment.

Travelers looking to visit this awe-inspiring monument can do so via a hiking trail in the mountains of the Serra de Estrela. It's sparsely visited, due to a secluded location and because few tourists are even aware of its existence. Just make sure to stay out of the water — you wouldn't want to get sucked down the hole!

The blog “Viagens à Solta” offers a detailed description of the hike and the scene at Covão do Conchos. They recommend visiting in the winter, when frozen ice transforms the spectacle into an otherworldly milieu. (And if you do visit in the winter, consider bringing waterproof shoes and dress appropriately for the cold.)

If Portugal isn't in your travel plans, you can still witness Covão do Conchos thanks to this breathtaking drone footage in the video above, which flies a viewer right up to the mouth of the hole.