Albert Barnes Commentary Jeremiah 38:14

"Then Zedekiah the king sent, and took Jeremiah the prophet unto him into the third entry that is in the house of Jehovah: and the king said unto Jeremiah, I will ask thee a thing; hide nothing from me." — Jeremiah 38:14 (ASV)

The third entry - There was probably a passage from the palace to the temple at this entry, and the meeting would take place in some private chamber close by.