Sunlight streams into Grubug Cave in Indonesia in this National Geographic Photo of the Day from the 2015 Traveler Photo Contest.
Ryan Deboodt photographs the world's largest cave with a drone. He describes the video as follows:
"Take an otherworldly journey through Hang Son Doong, the world's largest cave, by both ground and air. Filmed near the entrance and the first and second dolines (skylights) which are 2.5 and 3.5 km inside the cave respectively."