They literally "lowered Jeremiah down on ropes," but the word "threw" is an exaggeration to say that they treated him roughly. Your language may have another way of saying this. AT: "they ... roughly pushed him into the cistern" (See: [[rc://en/ta/man/translate/figs-hyperbole]])
This was an open area attached to the king's palace that was surrounded by buildings and in which they kept prisoners. See how you translated this in [Jeremiah 32:2](../32/02.md).