We took a boat tour out to Las Cuevas Marmol, or the Marble Caves, in Lago General Carrera, which is a large glacier-fed lake straddling the Chile/Argentina border (Argentina’s portion of this lake is named Lago Buenos Aires).

From atlasobscura.com

“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.”