Targum Yonasan: It is the ground (bottom cell). Rashi - it is not between the top and the bottom. [One of] the five bottom cells in the south had an opening to the outside. Later in this verse, he translated "Al ha'Tichonah" to be the middle; those were not open to the outside. `Here, ha'Tichonah means the middle of the five bottom cells [in the south]; it had the opening to the outside.

Rashi: The middle of the five bottom cells in the south had an opening to the outside. There were three openings to each cell ¹ . One was to the (cell on the) right, one to the left, and one on top (Midos 4:3).

Radak: The opening between the bottom cells and the middle cells was in the south, and also between the middle cells and the top cells.

Malbim: It was from the Heichal to the cells. We can say that the foundation of Bayis Rishon was six Amos, like that of Bayis Sheni. If so, the opening from the Heichal to the cells was to the middle (second tier of) cells, which was even with the floor of the Heichal. The verse does not discuss the opening from the cells to the outside. We can say that the foundation of Bayis Rishon was six Amos., like that of Bayis Sheni.

Rashi: It is the south side. ¹

Gra: It is the north side. It is to the right hand of one who enters the Heichal.

Rashi: It is a spiral staircase. Radak - it was within a hollow pillar.

Radak: It is an opening in the ceiling. We find (Menachos 34a) 'a Lul open from the house to the Aliyah (upper story).'

Rashi: It is like El ha'Shelishiyimm (to the third, i.e. the top tier of cells). Radak - it is plural, for there were many cells around the Bayis, in 3di.