A few weeks ago, Jeni, Maddy and I visited Liberty Jail in Liberty, Missouri. It was a great experience to see the location where D&C 121-123 were received by the Prophet Joseph. B.H. Roberts said that these revelations "made Liberty jail, for a time, a center of instruction. The eyes of the saints were turned to it as the place whence would come encouragement, counsel—the word of the Lord. It was more temple than prison, so long as the Prophet was there. It was a place of meditation and prayer. … Joseph Smith sought God in this rude prison, and found him” (B. H. Roberts, A Comprehensive History of the Church, 1:526).
There was an LDS visitor's center there and we received a brief tour of the history of the site as well as the construction of the jail, how it became a home at one point in time and how the Church purchased it, reconstructed it as a jail using the last remaining wall, and then built the visitor's center around it. The first two pictures below give you a good idea of how cramped they must have been as well as how deep the rock walls were. The last picture shows the jail as it stood in its original condition back in the 1800's.