Obviously: Here be spoilers lurking!
I read tEp and got rather confused when comparing the description of the Necron city with the sketch (also known as "map") at the end of the book. I am unable to wrap my mind around the description of the location and layout of the alcoves (though they might be anywhere) and more importantly the monolith field and the transport cirlce and finally the core. On p. 82 under monolith field there is a mention of a "ringed hall". Which ringed hall? The one labelled as "transport cirlce? Is the transport circle located under the core? Frankly, one picture would have told more than four paragraphs and it would have been nice to label all the stuff on the map. Am I lacking the ability to think in four dimensions?
And why should the space marines deactivate the core? They have no information whatsoever on its function and might even be so clever as to guess that the force field is helping to keep them safe from the oceanic pressure. What's preventing them from using the transport circle and not bothering about the strange crystal several hundred feet up in the air?
I would be glad if someone could help me out, I am about to enter a Tzeentchian pact!