Cave systems and underground trails have long been the source of fascination for scientists and explorers, and Vietnam's Hang Sơn Đoòng is one of the most amazing system that researchers from around the world have discovered just a few years ago.

The Hang Sơn Đoòng cave is the world's largest and it's just as grand as you'd imagined.

Tucked away in Vietnam's Phon Nha-Ke Bang national park, the cave was first discovered by a farmer in 1991.

Source: saffrontravel.net

But, it was never explored until researchers heard of it and ventured in, in 2009.

Source: oxalis.com.vn

Over 5 kms long and 200 metres high, the only way in is a 80 metre rope drop.

Source: en.hellovietnamtravel.com

A thick forest covers the entrance and bits throughout the tunnel.

Source: 500px.com

There is even a river with a fairly strong current flowing through.

Source: seaholidays.net

And, record-sized stalagmites.

Source: telegraph.co.uk

The cave is so huge, in fact, that there are even clouds inside.

Source: telegraph.co.uk

Got your next travel destination set?

Masthead Source: news.nationalgeographic.com, Feature Image Source: 500px.com