The lair is the rumored abode of Pazuzu in Hotel Harrison. The room by the gallery of Hotel Harrison is supposed to be where the demon is rumored to live. However, the room can't be accessed and doesn't exist other than outward texture.
However, a possible theory emerged in light of new evidence found by myth hunters. Ken Rosenberg's office is theorized to be haunted by the whispers coming from Pazuzu's Lair. The other side of the corridor of the hotel leading to Ken Rosenberg's office is covered in complete darkness and is ironically near the same room, which is said to be haunted by Pazuzu, thus this darkness is said to be Pazuzu's Lair. However, the myth is largely deemed as false by technical gamers.