Situated around 60 kilometers from Dong Hoi, the capital of Quang Binh Province in central Vietnam, the six-kilometer-long Dark Cave was discovered during the Vietnam War and used as a bomb shelter by local residents.
A 400-meter-long zipline over the Chay River to the entrance of the cave was installed in 2014.
"The interior of the cavern is unlit and the rocky walls are dark grey and black, and hence the name," SCMP said.
"It’s a short swim to get inside, followed by a guided walk (helmet with a headlamp provided), a mud bath and a kayak ride back to the starting point."
Surrounded by primary forests and limestone karsts, Dark Cave has become one of most popular tourist attractions in Quang Binh, dubbed Vietnam’s cave kingdom.
The other seven in the zipline list include the Shinta Mani Wild Resort in Cambodia, the Chocolate Hills Adventure Park in the Philippines, the rainforest in Laos, and the Mega Adventure theme park on Sentosa Island in Singapore.