The Sơn Đoòng Cave („Hang Sơn Đoòng“ means „Mountain River Cave“ in Vietnamese) appears to be one of the largest known caves on earth. It is situated within the Phong Nha-Kẻ Bàng National Park in the heart of Vietnam and was just discovered in 1991. The succeeding footage by Ryan Deboodt is breathtaking and should be enjoyed without any further introductory words:
Additional photographs are available within his blog posts of 2014: „Hang Son Doong“ and „Return to Hang Son Doong“. The Huffington Post has some more amazing photos: „World’s Largest Cave, Son Doong, Hosts First Public Tours (And The Photos Are Unreal)“. Of course the National Geographic also has an extensive article and a documentary.