As we were marching past a tall brick building a shout of derision saluted our ears, looking up we saw a number of men, clad in Confederate gray, looking at our sorry company and hurling epithets at us, which were too vile to repeat in these pages. This was the famous, or perhaps infamous is the better word, Castle Thunder. It was a penal prison of the Confederacy and within its dirty, smoke begrimed walls were confined desperate characters from the Rebel army, such as deserters, thieves and murderers, together with Union men from the mountains of Virginia and East Tennessee, and Union soldiers who were deemed worthy of a worse punishment than was afforded in the ordinary military prisons. Many stories are told of the dark deeds committed within the walls of that prison. It is said that there were dark cells underneath that structure, not unlike the cells under the Castle of Antonia, near the Temple in Jerusalem, as described in Ben Hur, into which men were cast, there to remain, never to see the light of day or breathe one breath of pure air until death or the fortunes of war released them. The horrors of the Spanish Inquisition in the middle ages were repeated here. Men were tied up by their thumbs, with their toes barely touching the floor, they were bucked and gagged and tortured in every conceivable way, and more for the purpose of gratifying the devilish hatred of their jailors, then because they had committed crimes. On we march past Castle Lightning, a similar prison of unsavory reputation, to Libby Prison, which opened its ponderous doors to receive us. But I will reserve a description of this prison for another chapter. CHAPTER III. LIBBY PRISON. “They entered:—’twas a prison-room Of stern security and gloom, Yet not a dungeon;”— The Lady of the Lake, Scott. Libby Prison, up to this time, was the most noted and notorious prison of the South. It was a large building two stories high on its north or front side, and three stories high on its south or rear side, being built on land sloping toward the James River. The building had been used before the war as a store for furnishing ship supplies. The upper story was used as a prison for officers. The second story was divided into three rooms. The east room was a hospital, the middle, a prison for private soldiers and the west room was the office of the prison officials. The lower story was divided into cook room, storage rooms and cells. It was down in one of these storage rooms, that Major Straight’s party started their famous tunnel. Over the middle door was painted