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. The best time of the year to visit the Marble Caves is roughly between September and February when the ice melts feeding the lake and the color of the water is particularly enchanting turquoise. In terms of hours, the best time to take a boat tour is early morning to catch the right lighting for great pictures. Know Before You Go There are ferries from Chile Chico that will take you to and through the Marble cave and its tunnels. The caves are based on a lake, and the only way to reach them is by ferry.