The doorway for the middle story was on the right side of the temple. They went up by stairs to the middle story, and from the middle to the third.
References for 1 Kings 6:8
So he built the temple and finished it, and he paneled the temple with beams and boards of cedar.
And he built side chambers against the entire temple, each five cubits high; they were attached to the temple with cedar beams.
Then the word of the Lord came to Solomon, saying:
"Concerning this temple which you are building, if you walk in My statutes, execute My judgments, keep all My commandments, and walk in them, then I will perform My word with you, which I spoke to your father David.
And I will dwell among the children of Israel, and will not forsake My people Israel."
So Solomon built the temple and finished it.
And he built the inside walls of the temple with cedar boards; from the floor of the temple to the ceiling he paneled the inside with wood; and he covered the floor of the temple with planks of cypress.
Then he built the twenty-cubit room at the rear of the temple, from floor to ceiling, with cedar boards; he built it inside as the inner sanctuary, as the Most Holy Place.
And in front of it the temple sanctuary was forty cubits long.
The inside of the temple was cedar, carved with ornamental buds and open flowers. All was cedar; there was no stone to be seen.
And he prepared the inner sanctuary inside the temple, to set the ark of the covenant of the Lord there.
The inner sanctuary was twenty cubits long, twenty cubits wide, and twenty cubits high. He overlaid it with pure gold, and overlaid the altar of cedar.
So Solomon overlaid the inside of the temple with pure gold. He stretched gold chains across the front of the inner sanctuary, and overlaid it with gold.
The whole temple he overlaid with gold, until he had finished all the temple; also he overlaid with gold the entire altar that was by the inner sanctuary.
Inside the inner sanctuary he made two cherubim of olive wood, each ten cubits high.