From the entrance of the Sanctuary, go down the stairs to the room on the left. It is located in the nest of Lis on the skeleton of Gaston Bellefort. Gaston had been searching for the Dark Brothehood Sanctuary for weeks and eventually found it. He attempted to infiltrate the Sanctuary, judging by his corpse in the Sanctuary, in vain.
My scribing tools are lost, and I've no time for a lengthy entry, anyway. It's taken weeks, but I finally found it! The Sanctuary of the Dark Brotherhood! One of them, anyway. In Skyrim, under a forest road.
I've been watching them, the assassins. Their comings and goings. The fools have no idea they're being observed. My next goal is to somehow make it past the sinister black door, into the Sanctuary itself.
I don't have time to even think about the dangers. The truth must be known!