Black Book of Nentruhn

Among the beacons of Nentruhn, a number of items exist that take the shape of large tomes. They are surrounded by an unseen dark magic that seals the books shut. What makes these tomes special among the creations of Nentruhn is that they can be used as stable gateways to travel to the realm of the deity-like voidsent. Each book is connected to one of the great libraries of knowledge that is part of Nentruhn’s realm. What exactly the purpose of these books remains unknown. However, many who worship Nentruhn search for these books, as they are the most reliable way to access the knowledge gathered by the voidsent.
A special ritual can be performed to unseal the book, allowing it to be opened. When the book is opened the pages will flip uncontrollably until they get to the page which contains the gateway to Nentruhn's Realm. This gateway appears as a pitch-black pool of liquid void. Any creature that touches this substance will have its mind dragged into the black book, its physical body remains behind.