Robert Silverberg is possibly the most underrated sf writers of all time, considering that he has been writing sf since the 50s, won numerous Hugo, Nebula and other major sf awards, and is a Science Fiction and Fantasy Writers of America Grand Master. In spite of all this he never seems to be "in vogue" these days, most of the younger generation of sf readers today have never read anything by him. I believe this is indicative of how criminally underrated he is and the ongoing decline of civilization as we know it.
What Silverberg does better than almost any sf authors writing today is to write short stand alone novels with very strange plots and excellent characterization. His special talent is to drop the reader right in the middle of a strange place and time of his imagining and gradually acclimatize you through his story telling skills.The Book of Skulls
is a very odd book, even among the very odd books he has written. The basic plot is very simple, four American college boys seek immortality in a monastery in the Arizona desert. The caveat being that of the four applicants only two will achieve immortality, the other two have to die, one by suicide and the other by murder. The simple synopsis belies the deep complexity of the book as we get to know each of the young protagonists through alternating first person narrative. Silverberg wrote this book during 1970 when written science fiction was being shaken up by the "new wave" of authors who were experimenting with new writing techniques, structures and often controversial contents (epitomized by the legendary [b:Dangerous Visions|600349|Dangerous Visions|Harlan Ellison|https://d.gr-assets.com/books/1176167292s/600349.jpg|2758790] anthology edited by Harlan Ellison). The Book of Skulls is a fine example of the sort of sf being written at this time. The story takes some very dark and bizarre turns with several long passages of the main characters' stream of thought, epic length sentences and the odd explicit sex scenes which are in no way titillating.
The book is not overtly sci-fi but it is ambiguous enough to be considered sci-fi under certain assumptions, under different assumptions it could be viewed as a social satire or dark fantasy. Certainly it is character-centric thought experiment, a work of speculative
fiction that can comfortably fit into our modern day's "weird fiction" subgenre. It was nominated for both the Hugo and Nebula awards (but won neither).
The book is very well written as is the case with most of Silverberg's output, the prose style may be less lyrical than a lot of his other books because it is written in the voice of young college students. Interestingly Silverberg has given each of the four narrators their own individual "voice" which may not be so noticeable to begin with but become quite distinct later on in the book.
If you are looking for galaxy spanning sci-fi, post apocalyptic sci-fi, cyberpunk etc. this book is not for you, but if you are in the mood for something weird and disturbing that will leave you wondering the hell the author just hit you with this could be just the ticket.