The icen door was formed to keep great evil contained and to keep the curious living. May E'ci walk beside you.
What does this information mean?
From the words of
Master T'Lys: "The Menagerie was a creation of an ancient arch-mage by the name of Miragul. It was his private residence and laboratory hidden within the Everfrost Peaks. Inside he kept many unique objects and creatures, much of them created by his own hand."
Slay everything in the first room to unlock the eastern door.
Slay A remenant of Miragul in the eastern room. ( -158, -24, -321 ) /waypoint -158, -24, -321
Examine the chests in the eastern room until you find an ancient scroll. Examine it to unlock the western door. (Note) I did not find a chest, but after clearing the room the western room was open.
Examine the book on the pedestal in the western room to make the cube at the center of the room interactable. ( -45, -24, -321 ) /waypoint -45, -24, -321
(Note): The book may not be accessible, as well as the cube but after clearing the room the northern door may open.
Examine the cube at the center of the room to unlock the northern and final door.
Kill Sulon McMoor in the northern room. ( -39, -24, -373 ) /waypoint -39, -24, -373
Examine the book on the pedestal in front of Sulon McMoor.
Slay Myrgoth who spawns after a few moments in front of the pedestal.