Moria East Gate and Mirrormere
They slept in the Twenty-first Hall. They were above and to the north of the Great Gates. (A Journey in the Dark; Bk1). They went north from here and found the Chamber of Mazarbu – Balin’s Tomb – on their right. After their battle with the Orcs here they escaped through the other door and down many flights of stairs covering about a mile in horizontal distance. (The Bridge of Khazad-dum; Bk 1).
This led them to the Second Hall. The narrow bridge from which Gandalf fell led from this Hall to a broad stair, along a wide road, through the First Hall to the Great Gates – about a quarter of a mile in all. (The Bridge of Khazad-dum; Bk 1). After Gandalf fell the others fled this way and finally came through the broken doors of the Great Gates to the open air. (Lothlorien,; Bk 1).