Well, just the title, really.
I've always pictured it as a network of pulsating green circular tunnels, a bit like the wormholes on Star Trek, except solid, so you can stand on it.
But if that was true, I wonder how could Commoragh be built? What are the foundations set in if the ground is impenetrable?
So I was wondering if perhaps it is more like the network the old ones built in Giantslayer, the Gotrek and Felix novel. More like wraithbone corridors of some appreciable thickness.
Is there any fluff on this?