See that tiny speck in the bottom right corner? That's a person—a very hard-to-see person, standing inside Vietnam's enormous Son Doong cave, the largest in the world. Photographer Ryan Deboodt ventured inside to get these astounding shots.

Amazingly, Son Doong cave was only discovered by locals in 1991. British scientists surveyed the 5.5-mile-long cave in 2009, revealing a main chamber over three miles long, 650 feet high and nearly 500 feet wide, significantly surpassing the previous record holder.

Guided tours of the cave began in 2013, on a very limited basis: only 224 people will be allowed inside this year. Visitors enter by rappelling more than 250 feet to the cave floor, where they spend three nights camping inside.

Photographer Ryan Deboodt tells Gizmodo that shooting in the Son Doong cave felt like being in an alien environment. "I always wanted to explore other planets and I think this might be the closest I can get to that experience," he says.

Shooting in such an alien, unreachable landscape has enormous challenges. "The environment is tough in caves and nothing ever seems to go as planned," Deboodt told us. "There is a lot of problem solving down there and so many points where it can go wrong: camera, triggers, flashes, bulbs, etc."

The environment is daunting, but Deboodt uses those challenges to create magnificent images. "Besides the light coming in through the entrances and holes in the ceiling, when photographing caves you have to create all your own light which can lead to out of this world photographs," he says.

Otherworldy, indeed. Check out more of Ryan Deboodt's breathtaking photography on his website and his Facebook page.