You pick up a book. The cover says "The Imperial Guide to the Librorum Infinitum". You flick to the page marked "Introduction" in the table of contents.
It is unknown where the Librorum Infinitum is. It is unknown how large the actual library is because no official blueprints or maps of the library have been found yet. That has not stopped people from trying to map it though. People who are in the library will often find that no two aisles of it are the same. Many people live within the library and small villages can be found inside the forests of the infinite library.
The Librorum Infinitum has what appears to be an endless supply of books and an endless variety of shelf types. Some shelves stretch so high as to be beyond the sight of the author. Sometimes books can appear from literally nowhere. The author believes it is the work of heretical mages who have not been authorized by the emperor's universities. A small minority of its tomes are written in the Emperor's English, some of it is written in the language of pre-colonial savages, and some of it is written in ways this loyal citizen could not dream of describing properly.
The library is not always safe for humans. All manner of beast may be found within its halls and not all of them are friendly. For example, there are spiders that are about half as tall as the emperor himself here who have killed many a denizen or worse. There are also perversions of man that can be found walking its halls, organizing its books.
The scenery of the library is variable. One can find literally any kind of environment within its halls. Deserts, jungles, lakes, plains, oceans, and everywhere one can find people searching for something if they look hard enough. The author always hopes to find a loyal citizen of the empire but they are few and far between, it seems. Despite the emperor's massive reach they can not dream of amassing a force that could conquer this land.
-A loyal servant of the Empire of Worlds