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 6,000-plus 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.
Source : WikiPedia