The original Half-Life was created with a modified Quake2 engine. This means that Quake console codes work in HL1.
How to access the console. OLd skool {HL installed in Sierra file}
How to use the console, Half-Life2: Use this link.
Find the shortcut icon that loads up Half-Life.
Right click it and copy.
Drag the copied shortcut onto your desk-top.
Right click the new shortcut and select properties.
The properties dialogue for the shortcut will come up. The first available text box, marked Target, is what you'll want to edit.
The default value here is the path and executable of Half-Life.something like:C:\games\half-life\hl.exe.
You need to change this too:C:\games\half-life\hl.exe -dev -console.Just add -dev -console to the end of what is already there. Note, there is a space before the -dev and -console.
NB: The -dev causes the game to start in develpers mode, with the console activated.
Loading the game via this edited link causes HL to load to a green and black screen. To enable cheat codes type: /sv_cheats 1 hit return key and then esc. Half-Life should load.
To use the console in game (first enable it, by editing the target line) hit the console key...which in the USA is the ~ key, in the UK it is ¬ (to the left of the 1).
Then type in the code you want to use:
Type in: /god (you don't die!)
/thirdperson (see Freeman) /firstperson (back to FPS)
/impulse 101 (get all weapons)
/noclip (walk through walls and fly)
/notarget (monsters don't attack you)
/map xxx.bsp (you need the map code, but you can load any map via the console)
Ok, here is a list: Bring down the console and type in
/god [return]
/map c2a1a[return]
/noclip [return]
/impulse 101 [return]
/give monster_gargantua [return] [esc]
You have now spawned a garg. Press esc to take a look and then bring down the console again and type in: /noclip [return] and esc.
Half-Life maps:
Black Mesa Inbound:c0a0,c0a0a,c0a0b,c0a0c,c0a0d,c0a0e