The first floor of Blackmoor Hall, where the Thorpe family live. In addition, at the heart of the first-floor landing lies the master bedroom, Jane Weston's room.
The stairway from the main hall leads up to the first-floor landing, and on either side are around twenty windowless guest rooms, although in the design, it shows more like thirty, this was a rough sketch, done roughly around two years before I published the novel, so one or two details did change in that time.
As you can see, turning left at the top of the stairway, at the end of the block of rooms, is a short walkway that leads through to the corridor - the one where Abi and Harry walk down on their midnight mission, where they feel like they are being watched. On the night of the Ghost Hunt, Kate leaves the apartment, stares at the space at the end of that corridor, and doesn't want to walk to the other end, for reasons she cannot explain. Instead, she used the door at the other end of the corridor, which brings her out near the master bedroom.
On the opposite side of the house lies an almost identical corridor, where the five nursery rooms, all in different colours, are located, but a doorway halfway down the passageway splits it into two.