Game Modes
Purchase The Long Dark Steam Key (referral link): Interloper is the hardest mode in Sandbo. Mods are only compatible with Steam versions of the game for Windows currently. If you are looking for mods for TLD v1.56, they are here. This website is is no way affiliated with Hinterland Games and only aims to provide easy access to published mods for the game.
Story Mode is the episodic main-game contained within The Long Dark, and is the only version of the game which contains an overall plot and NPC's.
Sandbox Mode is an open-play game mode, where the only goal is to survive for as long as possible. There are no quests to complete, and no NPC's to interact with (other than wildlife.)
Challenge Mode is a goal-oriented game mode that takes place on the sandbox-mode maps. Each challenge presents the player with a different challenge or hardship to overcome, but otherwise takes place in an open world environment.
Successfully complete the indicated task to unlock the corresponding achievement. To view your achievements and stats in Steam, select 'Community', 'My profile', 'View all my games', then the game and view stats.