Uber Geode News:  This cave is now also connected to the rainforest crater via a new tunnel.
Uber Geode
Uber Geode

This is the (nearly) mile-long, cave network, main antechamber which serves as the foyer connecting the surface hemisphere's Sotu perimeter and F.A.U. Crater to the long stretch of the Underway.  Even the annex-chambers of this attraction are so vast and towering that they contain lakes.  * In the Outlands, however, the Underland's cave chambers are so vast they contain oceans.

Regarding the Outland Realm for which this Construct is Themed:
The Underland is actually a nice place.  You'd be surprised.  There are geodes as big as cities and seas, and caves that weave through our crust to connect everything under us and then some; tons of bioluminescent life of every shape and size, and there's typically far less violence in the caves than Hollywood's films would suggest.  Most of the violence is in the uppermost levels closest to the surface where all the human radiowaves and other 'negative' energies are still prevalent.

Dimensions & Layout:
This giant cave chamber is an ellipsoid measuring nearly a mile along its z-axis, and nearly half a mile along both its x- and y-axes.  One of its ends is dominated by a corkscrew of the G.A.H., connecting it to the Inisfreeans surface and, as mentioned above, to the perimeter of Sotu.  Its opposite end swoops down into a drain-like opening which becomes the start of the Underway, and everything in between these ends consists of glowing crystal clusters of every color of the rainbow, sparkling waterfalls hugging and racing down the curving chamber's walls, and geode inlets so large that you can put a three-story house in any of them.  The crystals protruding from the walls of this chamber, including its stalactites and stalagmites, are so large, in fact, that you can climb and walk out on them.