The Library
Standing off the eastern border of the Market is The Library. A modest structure, by all external appearances, it doesn't seem very impressive. In fact, any of you from places with such a thing will probably realize your neighborhood's branch of the Public Library dwarfs this tiny structure.
Step inside and you quickly realize appearances are deceiving. Four floors rise above you, balconies over-looking the central entrance.
Halls branch off from the center and seem to stretch on for miles, all lined with shelves and shelves, rows and rows, of books.
In the library, if one were to spend enough time (you do have all the time in the world, after all), one can find record of anything ever written down, in your world, in other worlds. Mysteriously, all records regarding Greece and Greek Myth are missing…
The Library is prone to changing, halls will move, entire floors will switch while you're still there, so do try not to get lost in it. The only thing that consistently stays the same is the basement below the library, the door to this basement is however exceptionally hard to find. Inside the basement is Hades' record hall, containing records of deceased people from all worlds.
Note: One notable feature of the library is the uncanny ability to find exactly what you were looking for when you arrived. No one's advertising this little feature, of course, and certainly not the gods.