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Carved into the Patagonian Andes, the Cuevas de Mármol are located on a peninsula of solid marble bordering Lake General Carrera, a remote glacial lake that spans the Chile-Argentina border. 

Formed by more than 6,000 years of waves washing up against calcium carbonate, the smooth, swirling blues of the cavern walls are a reflection of the lake's azure waters, which change in intensity and hue depending on water levels and time of year. 

Located far from any road, the caves are accessible only by boat. Thirty-minute tours are operated by a local company, weather and water conditions permitting. More photos of the Marble Caves can be seen on Atlas Obscura.

The Cuevas de Mármol are but one of many caves where the interplay of light and water create a spectacular visual display. Here are a few of our favorites.

• Gruta do Lago Azul, one of the largest flooded cavities on the planet, littered with prehistoric animal bones.
• The Blue Cave of Bisevo, an ethereal blue ocean cave in Croatia
• Grotta Azzura, the glowing swimming hole of Emperor Tiberius