Had come to is best understood as causative, “had been put in.”

What is meant by the dungeon cells is unclear; apparently Jeremiah had been placed in some kind of underground dungeon.

Many days is a typical Hebrew expression referring to an indefinite and long period of time; several versions have “a long time.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on Jeremiah. (UBS Helps for Translators). New York: UBS, 2003. For this and other handbooks for translators see here .