Access to this dungeon is complicated, see quest for details. The gland flag lasts two hours, once you have passed through the portal at the end of the Sealed Olthoi Passage (Map available at ACMaps.com) at least once, you can reenter the lair using a backdoor portal located in a burrow at 44.5N 57.3E just east of Paradox-touched Valley. There is a door just before the portal that is opened by using the Olthoi Cistern in the far right corner of the Lair on a small platform.