Mishnayos Middos Perek 4 Mishnah 5

The mesibbah (a winding walkway) went up from the north-east corner to the north-west corner by which they used to go up to the roofs of the cells. One would ascend the messibah facing the west, traversing the whole of the northern side till he reached the west. When he reached the west he turned to face south and then traversed whole of the west side till he reached the south. When he reached the south he turned to face eastwards and then traversed the south side till he reached the door of the upper chamber, since the door of the upper chamber opened to the south. In the doorway of the upper chamber were two columns of cedar by which they used to climb up to the roof of the upper chamber, and at the top of them was a row of stones showing the division in the upper chamber between the holy part and the Holy of Holies. There were trap doors in the upper chamber opening into the Holy of Holies by which the workmen were let down in baskets so that they should not feast their eyes on the Holy of Holies.