Photo and caption by Chris Miller / National Geographic Traveler Photo Contest

Location: Hang Son Doong, Quang Binh, Vietnam

The photographer says: "Hang Son Doong is located in central Vietnam and is the world's largest cave. It was only explored for the first time in 2009 and is just now opening up to very limited tourism. This photo shows some members of our party beginning the climb up one of the two collapsed roof sections or dolines that are prominent features in the cave. The vegetation that can be seen is entirely inside the cave, with the real jungle floor some 150m further above. Two-way radios and a laser pointer were used to get people in position and to ensure their headlamps provided just the right amount of illumination."

3. Sunrise at Seoraksan, South Korea