Download

Click here to download the SI installer.

Or try here if the installer gives you trouble.

SI is a Half-Life mod. You need Half-Life installed to play it.

Extract the archive to your Half-Life directory in Steam.

When the mod is installed, your folder structure should look like this:

Steam/SteamApps/common/Half-Life
├── htmlcache
├── platform
├── si
├── valve
├── valve_hd