Biggest Underground Chambers

It is rather difficult to determine the biggest chamber. First it's a problem how to measure its dimensions, and then it's a problem to decide which aspect of the survey data is most significant.

How do you measure the size of an underground chamber? In caves, it is rather difficult to determine exact volumes, as surveying just follows a single line. You just get a sort of skeleton of the cave. The solution to measure surface and volume is to add the distance to walls, floor and ceiling. You measure to the wall as often as possible. In big chambers you may survey once along the wall. The height is determined using a thin rope and a gas filled balloon. This is also done as often as possible. The result is nevertheless very inaccurate concerning volume, but length and width are quite accurate.

As a result it is actually impossible to make a sort of ranking based on survey data. While volume would be the best criteria for this, it is also the least accurate number. This changed in recent years with the introduction of 3-D laser scanners. They allow the scan of all walls and ceiling and the construction of a computer model. Unfortunately the technology is very expensive and the survey is a lot of work. While currently only a dozen caves was scanned so far, this might become the main surveying technique for such huge caverns in a few years.

The official list is linked below. Our topic is tourist sites, and so we made an excerpt. The two biggest chambers plus all which are accessible in any way. We were astonished how many on Bob's list with 38 chambers were actually show caves.

Name	Cave Name	Location	Length	Width	Height	Area	Volume	Description
Sarawak Chamber	Good Luck Cave	Gunung Mulu National Park, Sarawak, Malaysia.	641 m	429 m	113 m	154,530 m²	9,670,000 m³	This is the biggest cavern (the biggest single chamber) of the world, accessible only to cavers
Miao Room	Gebihe system	China	824 m	336 m	177 m	140,540 m²	10,570,000 m³	This is also the biggest cavern (the biggest single chamber) of the world, accessible only to cavers
main passage	Phong Nha Cave	Phong Nha-Ke Bang National Park, Quang Binh Province, Vietnam	3,100 m	80 m	180 m	m²	m³	This is also the biggest cavern (the biggest cave passage) of the world, accessible on cave trekking trips
Majlis Al-Jin	Majlis Al-Jin	Oman	320 m	225 m	120 m	61,000 m²	4,090,000 m³	A karstfenster in the middle of a huge chamber, can be seen from the rim.
La salle de La Verna	Gouffre de la Pierre Saint Martin	France	255 m	245 m	199 m	43,000 m²	3,650,000 m³	Easily accessible through a tunnel, but no further development and no light.
Salon de Gigantes	Grutas de Bustamante	México				39,730 m²		show cave
main passage	Gua Payau (Deer Cave)	Gunung Mulu National Park, Sarawak, Malaysia.	870 m	177 m	270 m	38,600 m²	6,310,000 m³	show cave
main passage	Kocaín Mağarası	Mediterranean Region, Turkey	m	m	m	37,200 m²	m³	not developed but easy to visit
Big Room	Carlsbad Caverns	Carlsbad Caverns National Park, New Mexico, U.S.A.	1,200 m	190 m	78 m	33,210 m²	m³	show cave
main chamber	Grotta Gigante		240 m	138 m	132 m	33,120 m²	m³	show cave
Martel's Chamber	Skocjanske Jame (Skocjan Caves)	Slovenia	308 m	123 m	146 m	32,090 m²	2,200,000 m³	not part of the show cave, but the show cave is only slightly smaller
main chamber/passage	Phu Pha Petch Cave	Satun GeoPark, Satun Province, Thailand	623 m	150 m	58 m	30,500 m²	m³	show cave