Langley Hall

"The Last Lamp-Post gleams through the fog; the furthest-flung piece of London."

"A house of numberless rooms and diverse guests. Founded by Lord Langley, it is a refuge for those willing to brave the dark."

"A cottage the size of a cathedral. Mellow candlelight shines through its frosted windows like spilt treacle."

"Here, the vanished Lord Langley founded a home away from home; a London for the exiled, the lost and the lovelorn. Distance is suspended inside; no one has ever claimed to have charted the entirety of the limitless hall."

Langley Hall is a mansion in Eleutheria built by the eponymous Lord Langley. It's somehow bigger on the inside than on the outside; Lord Langley himself is said to be lost in its labyrinthine structure. Those who leave the building after a night or two there have an unnerving desire to return immediately.

What the mansion used to be, and why visitors keep returning [Spoilers for "Looking for Lord Langley"]
The mansion is heavily implied to be built from the remains of the original Scrive-Spinster library. The Halved tasked Lord Langley with building a sanctuary from the remains of the library, for reasons that remain unknown. Tourists keep coming to the Hall because Lord Langley's body is inscribed with Correspondence sigils that attract people.