For HL2:
Place in your "steamapps/common/Half-Life 2/hl2/maps" directory.

Boot HL2

Open the in-game console and type:

map hirohouse

Enjoy!


For SFM:
Place in your "steamapps/common/SourceFilmmaker/usermod/maps" directory.

Boot SFM

File/Load Map

(IMPORTANT- FROM CAMERA START POINT, PRESS SHIFT+W+A+Z AND HOLD UNTIL THE MAP IS VISIBLE. I'LL PROBABLY FIX THIS GLITCH SOONER OR LATER.)

Enjoy!


For GMOD:
Place in your "steamapps/common/GarrysMod/garrysmod/maps" directory.

Boot GMOD

Load it through the "Start New Game" section in "Other" tab

Enjoy!