Hidden Mysteries: Civil War is a video game which involves hidden objects where players have to find objects that are hidden in the game screen. The game's background is set during the American Civil War. The player has to look for clues in actual Civil War battlefields. The player has to search for letters which contain clues about hidden treasures. 18 locations in the game are actual locations of battles in the Civil War. There are also more than a hundred hidden objects to look for in each level. There is also a Cannonball mini game that is inspired by the classic game of minesweeper.
There are two modes in Hidden Mysteries: Civil War. These are Timed mode and Relaxed mode. Players race against the clock in Timed mode, and are allowed to finish the game with no time limit in Relaxed mode. There are three hints in each period. Clicking the hint makes the screen glimmer, which notifies the player of the item's location. Players are free to switch from one location to another by clicking on the "maps" option. Each level also has a letter with coded message. The coded message comes in the form of symbols. Users have to match symbols with their corresponding letters to decipher each letter's message.