The Marble Caves, also known as the Marble Cathedral, are a geological formation of sculpted marble on the General Carrera Lake in Patagonia. These caves are only accessible by boat, offering a unique experience to witness the stunning blue waters reflecting on the marble walls. Tours are typically available from nearby towns like Puerto Rio Tranquilo. Accessibility can be limited due to weather conditions, especially during winter months (June-August) when boat tours might be suspended due to rough waters and ice. Guided tours are highly recommended for safety and navigation. The cost can vary depending on the tour operator and duration, but expect to pay around $50-$100 USD per person. A typical visit lasts about 2-4 hours including travel time by boat. Check weather conditions and book in advance, especially during peak season (November-March).