With the book you can now sense the shadow connections between this world and the wider cosmos.
You gain a better understanding of this strange world, and how it fits, or doesn't. Outside of something actually built by the demi-lich...who himself could travel without such a portal as a being of corrupt energy...its unlikely that the denizens of this world would build such a portal. Though there "technology" may have brought them close.
On the other hand, the massive desolation the natives inflicted on themselves would have created cosmic rifts, through which the great necrotic energy leaked into other worlds.
However you think the shielding of this place, which has kept you from being killed by radiation, may be interfering (or is it all the radiation outside?).
Robot1 seems to calculate what you are trying to do: "Beyond whatever you have found here, the members of the Brotherhood of Thought seemed to have gathered the only other relevant data we know of on the cosmic travel you may wish to undertake." "Of course, they have not actually helped you make the trip. At this time."
EDIT: This all takes some time, and Buckthorn and Forge start to get hungry.