In House of Thule, Upper Floors: Located at the zone-in of the western half of the zone (Al'Kabor/Miragul side).
In House of Thule, Upper Floors (group instance): Lilth is involved with the group task "Redemption" (see this quest entry for information).
In House of Thule, Upper Floors (raid instance): Part of the raid event "Guardian of the House" (see this quest entry for event and loot information).