See here. The Son Doong Cave. Discovered last year by a local man and explored and assessed this month by a team of British explorers.
Any spelunkers out there?
Ah.
No mention of the Elder Ones.
Then…the true largest cavern is still secret.
Veerrrry gooooddd…carry on, sub-creatures.
The Hour of your Doom has not yet arrived.
Not…yet…
Mammoth Cave in Kentucky has more than 360 miles of passageways and new areas are discovered and added each year. That translates to 580 kilometers. I don’t even know if it is the largest. Perhaps the overall capacity of the one mentioned in the OP is greater.
I think you are confusing the overall length of a cave system with the size of a particular cavern. I think this find is of a single cavern 5km long, 200m high and 150 wide.