Slenderman's Shadow is a horror adventure game based on the indie game Slender. Avoid Slenderman and collect all the notes to win the game. The action takes place in an abandoned sanatorium where Slenderman will follow your every move and try to stop you from finishing your quest. Avoid him at any cost or feel his wrath.

Sanatorium is the 1st map in the Slenderman's Shadow series. Like the game it is based on, Slender, the goal is to collect 8 pages scattered in a derelict asylum, instead of a forest. The pages are located about the facility, but unlike Slender and future installments of the series, the pages do not move or randomize to different parts of the map.

Your character is armed with nothing but a flashlight, similar to the original Slender. The flashlight is capable of illuminating anything in front of you, and is controlled with the camera controls. The player is armed with no other items, and has no defense until the player can collect the 8 pages. Once that happens, the player can take out a pistol and attempt to shoot the Slender Man, but this has been removed in the newer versions.

The player must collect all 8 pages before being captured by the Slender Man. Fortunately the pages stand out very brightly and are very easily visible.

In the Unity remake, pages do randomize and have changed to a brown colour, sometimes difficult to see.