To access the newly added map, you must load it via the console (instructions below).
Installation and usage
2. Extract athec_mod_a07.rar to C:\Program Files (x86)\Steam\SteamApps\SourceMods
3. Restart Steam if the application is currently running. The modification (titled "Above the Catacombs (a07)") should be available for launch under the "Games" category on your Steam client. You may wish to add "-novid" (no quotations) to the program's launch options, this will skip Valve's default intro. You can modify your launch options by right-clicking on "Above the Catacombs (a07)" and clicking on "SET LAUNCH OPTIONS..."
4. If you want to try out the new map (highly unfinished!), open up the console by pressing ~ (make sure you have the developer console enabled) and type the following: