Legends say that there was once a prosperous kingdom ruled by a mighty monarch, his powers bestowed upon him by a magical spear. Years have passed and the kingdom was completely destroyed, save for a mysterious citadel in the midst of a dangerous forest. A young explorer travels there and discovers the entrance. However, once inside the citadel, a strange old man seals the doors, trapping the explorer and compelling him to climb to the top of the gigantic structure in order to escape.
Shadow Tower: Abyss is a sequel to Shadow Tower. Like its predecessor, it is a first-person action role-playing game with a heavy emphasis on dungeon crawling and a setting that mixes medieval fantasy with horror. Most of the elements distinguishing the previous game have been carried over, including survival-oriented mechanics with features such as weapons gradually deteriorating when used in battles. As opposed to the first game, the player character can wield guns such as pistols, sniper rifles, etc., though ammunition is comparatively scarce. It is also possible to switch between firearms and melee weapons during combat, as well as target specific body parts of the enemies.
The protagonist collects souls while exploring areas and defeating monsters. These souls gradually increase his strength, allowing him to inflict more damage. Most other parameters, however, are upgraded by finding, consuming, or equipping various items. Weapons proficiency is divided into break, pierce and slash categories. Compared to the predecessor, the sequel has a larger variety of areas, its citadel hosting entire cavern systems and even underground forests.