Commentary for Middot 4:5
וּמְסִבָּה הָיְתָה עוֹלָה מִקֶּרֶן מִזְרָחִית צְפוֹנִית לְקֶרֶן צְפוֹנִית מַעֲרָבִית, שֶׁבָּהּ הָיוּ עוֹלִים לְגַגּוֹת הַתָּאִים. הָיָה עוֹלֶה בַּמְּסִבָּה וּפָנָיו לַמַּעֲרָב. הָלַךְ עַל כָּל פְּנֵי הַצָּפוֹן, עַד שֶׁהוּא מַגִּיעַ לַמַּעֲרָב. הִגִּיעַ לַמַּעֲרָב, וְהָפַךְ פָּנָיו לַדָּרוֹם. הָלַךְ כָּל פְּנֵי מַעֲרָב עַד שֶׁהוּא מַגִּיעַ לַדָּרוֹם. הִגִּיעַ לַדָּרוֹם, וְהָפַךְ פָּנָיו לַמִּזְרָח. הָיָה מְהַלֵּךְ בַּדָּרוֹם, עַד שֶׁהוּא מַגִּיעַ לְפִתְחָהּ שֶׁל עֲלִיָּה, שֶׁפִּתְחָהּ שֶׁל עֲלִיָּה פָּתוּחַ לַדָּרוֹם. וּבְפִתְחָהּ שֶׁל עֲלִיָּה הָיוּ שְׁנֵי כְלוֹנָסוֹת שֶׁל אֶרֶז, שֶׁבָּהֶן הָיוּ עוֹלִין לְגַגָּהּ שֶׁל עֲלִיָּה. וְרָאשֵׁי פִסְפָּסִין מַבְדִּילִים בָּעֲלִיָּה בֵּין הַקֹּדֶשׁ לְבֵין קֹדֶשׁ הַקֳּדָשִׁים. וְלוּלִין הָיוּ פְתוּחִין בָּעֲלִיָּה לְבֵית קֹדֶשׁ הַקֳּדָשִׁים, שֶׁבָּהֶן הָיוּ מְשַׁלְשְׁלִין אֶת הָאֻמָּנִים בְּתֵבוֹת, כְּדֵי שֶׁלֹּא יָזוּנוּ עֵינֵיהֶן מִבֵּית קָדְשֵׁי הַקֳּדָשִׁים:
The Winding Ramp rose from the northeast corner to the northwest corner, by which they used to go up to the roofs of the cells. He would go up the Winding Ramp facing west and traverse the entire northern [side of the building], until reaching the west [side of the building]. When he reached the west, he turned to face south, and then traversed the west side until reaching the south. When he reached the south, he turned to face the east, and he then traversed the south side, until he reached the opening of the upper story, for the door of the upper story opened to the south. In the opening of the upper story, there were two poles of cedar, which they used to climb to the roof of the upper story. The ends of the beams divided the upper story between [the area above] the Holy [part] and the Holy of Holies . There were shafts open in the upper story into the Holy of Holies by which artisans were lowered down in boxes, so that their eyes should not gain pleasure of the Holy of Holies.
Bartenura on Mishnah Middot
English Explanation of Mishnah Middot
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.
Sections 1-4: The mesibbah was the walkway that they would use to get to the top of the Hekhal. The mishnah explains how the priest would walk on the mesibbah which began on the northeastern side (as we learned in mishnah three) and went to the northwestern side. He would then turn south (left) and walk to the end, then he would walk all the way to the southeastern cornet to get to the upper chamber that was built on top of the Hekhal and the Holy of Holies. The door of this chamber was open on the southern wall.
Section five: There were poles in the upper chamber which they could use to climb up to the roof. On the roof there was a division made by a wall of stones to distinguish between the Hekhal (the holy) and the Holy of Holies.
Section six: There were trap doors in the roof of the Holy of Holies through which they would let workmen down in baskets to fix the walls of the Hekhal and Holy of Holies when necessary. The workmen were let down in baskets that were covered on three sides so that all they could see was the wall that they were repairing. This would prevent them from unabashedly gazing at the Holy of Holies which would be considered an inappropriate means of deriving benefit from the holiest point of the Temple.