You play as a nameless protagonist who is tasked with killing the Minotaur and taking the Treasure of Tarmin.
The gameplay in Treasure of Tarmin consists of navigating through a series of 11x11 mazes and slaying the monsters that reside in them. Starting off with a weak bow and arrow, players must fight their way through the dungeon, picking useful items as they go, including weapons, armor, food, and treasure.
- Skeletons are the easiest enemy to defeat that attack the player's War Health. They come in both cloaked and regular varieties, the latter being easier to defeat.
- Giants are harder to defeat than skeletons and may or may not have shields. Giants attack War Health.
- Giant Ants are the easiest enemy to defeat that attack the player's Spiritual Health.
- Dwarfs attack the players Spiritual Health and may or may not have shields.
- Giant Scorpions are tougher than Giant Ants and attack the player's Spiritual Health.
- Giant Snakes attack the player's Spiritual Health and are harder to defeat than Giant Scorpions.
- Alligators are more powerful than Giant Snakes and attack the player's Spiritual Health.
- Dragons are the hardest enemies to defeat that only attack the player's Spiritual Health.
- Ghouls only appear late in the game and randomly attack either Spiritual Health or War Health.
- Wraiths are the more difficult version of Ghouls. They can appear with or without a shield.
- Door Monsters are special enemies. They appear as doors that open onto a blank wall and spawn only in the dungeon's lower levels. The Blue Door Monster, when defeated, drops a book that allows the player to teleport through walls. The Purple Door Monster's book turns any weapon or treasure to platinum, increasing its value to the game's maximum. Finally, killing the Pink Door Monster earns the player a book that gives him the ability to see through walls.
- Bombs may be hidden in treasure chests and bags. They explode the reduce the player's War Health.
- The Minotaur is the game's only boss enemy and appears as purple color in the game. The Minotaur attacks both Spiritual and War Health.