Is it mandatory to book accommodation inside Torres del Paine National Park in advance?

Yes. To hike the W Trek or the O Circuit in Torres del Paine National Park, you must have confirmed bookings for all campsites or refugios along your itinerary before entering the backcountry. Access to multi-day trekking routes is not allowed without prior reservations, and park authorities check bookings at control points. It is recommended to book 8 to 6 months in advance, especially during high season.