Thief Gold missions
Navigate to the Thief Gold install folder, and create an FMs subfolder. Navigate to it.
Extract the .zip into its own subfolder within the FMs subfolder.
Edit cam_mod.ini in the Thief Gold install folder, and change the line ;fm to fm (i.e. remove the semicolon).
Launch Thief Gold, and select the mission from the list.
Half-Life 2 / HL2 Episode 2 / Team Fortress 2 maps
In Steam, right-click the game; choose Manage > Browse Local Files
Navigate to the hl2/maps subfolder (create the maps subfolder if it doesn’t exist).
- for HL2 Episode 2, navigate to the ep2/maps subfolder instead.
- for Team Fortress 2, navigate to the tf/maps subfolder instead.
Extract the .bsp file from the zip file into the maps subfolder.
Launch the game. Enable the console with Options > Keyboard > Advanced > Enable Developer Console.
Press ` (backquote) to open the console. Type map mapname