At a length of some 9 kilometres (5.6 miles), Hang Sơn Đoòng in Vietnam, near the Laos border, is the largest known cave in the world. Inside is a large, fast-flowing river; its own microclimate; a chamber 5 kilometres (3.1 miles) long, 200 metres (660 feet) high and 150 metres (490 feet) wide; and some of the world's biggest stalagmites, some of them up to 70 metres (229 feet) high.
That is taller than One Franklin Square in Washington, DC, which stands 64 metres (210 feet) high.
Consider those proportions. Now consider the brave man -- photographer Ryan Deboodt -- who explored it with a DJI Phantom 2 quadcopter, a Canon 6D DSLR and EF 16-35mm f4 wide-angle lens, and a GoPro Hero4 Black to create a breathtaking video of this natural wonder for Oxalis, the company that will be taking guided tours into the cave.
He took his equipment to film at three different locations -- the entrance of the cave, and two dolines -- sinkholes that have formed into natural skylights -- at 2.5 kilometres and 3.5 kilometres into the cave.
"It's incredibly difficult to put into words how amazing Hang Sơn Đoòng really is," Deboodt wrote on his blog. "From the sheer size of the cave to the two dolines where plant life has started growing inside the cave. It is truly otherworldly and something that probably can't be experienced anywhere else in the world."
The team spent a long, 10-hour day exploring the cave, allowing Deboodt to capture some stunning photographs, as well as enough footage for a six-minute video.
"We also were incredibly lucky to witness sunbeams in Hang En the last morning we were there. At first we didn't think it was going to happen as with was cloudy and foggy outside," Deboodt wrote.
"Everyone decided to call it and head back towards civilization, but I wanted to stay and [team member] Thanh was kind enough to stay back with me. When the clouds broke and sunbeam started forming my breath was taken away. It was an absolutely incredible sight."