It is. The invitation will mention what books we have on the matter, if any. Those who receive the invitation will then decide if it's worth risking life and limb for, and if they agree, they are transported to the Library.

( so unfortunately it isn't as simple as walking in. )

You could say it's more of a private collection than something open to the public on ordinary days. ( most of the time you can't even get near it, but lately... ) I thought we became fairly well-known in the City, but I suppose there might still be people who hadn't heard of us.