Rare Stereo 3D Antique 1860s Tintype Photo Civil War Jail Western Outpost? For Sale

Interesting 1860s stereo tintype showing an unidentified fort like structure, with high, timber walls with the crossbeams on the outside.. usually to make it easier to keep people from getting out! There is what might be an armed guard standing watch in the tower, which has what looks like an arrow style weather vane on its roof.
Dimensions are about 7" x 3.5". Light and medium bends and a few dings. My scan might look a little grainy due to scan quality loss, but the actual tintype is fine.