https://store.steampowered.com/app/35140/Batman_Arkham_Asylum_Game_of_the_Year_Edition/

Critically acclaimed Batman: Arkham Asylum returns with a remastered Game of the Year Edition, featuring 4 extra Challenge Maps.
The additional Challenge Maps are Crime Alley; Scarecrow Nightmare; Totally Insane and Nocturnal Hunter (both from the Insane Night Map Pack).
Utilize the unique FreeFlow™ combat system to chain together unlimited combos seamlessly and battle with huge groups of The Joker’s henchmen in brutal melee brawls

Activating the steam key

1) You must download and install Steam http://steampowered.com/download/SteamInstall.msi (if not already installed).
2) Create a new account on Steam or go to an existing one.
3) Select "Activate via Steam ..." in the "My Games" section, and enter the key received after payment.
4) After activation, the game will appear in your list of games and you can install it.

Please leave feedback after successful activation of the game.