The only thing bigger than this infinite cave is the wait list.

By Melanie Lieberman
August 23, 2016
Barcroft/Getty Images

Vietnam recently opened its mammoth Hang Son Doong cave to intrepid travelers—and there's already a two-year wait list to visit.

Only one tour operator, Oxalis Adventure Tours, is authorized to lead expeditions deep into the caves beneath Phong Nha-Ke Bang National Park.

Also known as the Mountain River Cave, Hang Son Doong is a massive underground passage that is more than 3 million years old and reaches 300-feet across at its widest point—spacious enough to accommodate the new wide-body Airbus A380. At its tallest point, the cave reaches higher than 600 feet—high enough to accommodate a New York City skyscraper.

Oxalis’ 2017 tours were posted last week and sold out in only 20 hours, according to The Telegraph. Eager explorers will now have to wait until next year to even see the 2018 dates.

In an attempt to limit protect the delicate ecosystem, only 500 visitors are allowed to enter in a given year.

If you’re lucky enough to snag one of 10 spots on the next open tour, expect to drop $3,000 for a six-night trip, which includes trekking across the jungle, crossing the vast Rao Thuong River, scrambling, and rock climbing. Inside one of the world’s coolest caves, you’ll discover 100-foot-wide skylights from collapsed cave ceilings and even white sand beaches.

In the meantime, check out this extraordinary drone footage of the so-called “infinite” cave, which is perhaps the only way to see the stalactite-filled chambers and underground jungles until at least 2018.

Melanie Lieberman is the Assistant Digital Editor at Travel + Leisure. Follow her on Twitter and Instagram at @melanietaryn.