Half-Life Cheats

In the options screen under codes, enter the following, push a to confirm then go into trigger codes and turn it on. It told me this after I beat the blue shift game.

By completing the training mission you will receive this code. Under Options select Enter Codes, using the three word wheels make them show the proper phrase and hit A to verify.

Input this at the Secrets section, by moving the three bars up and down until they spell out this "sentence"

Enter these Passcodes to unlock the corresponding level

Enable this code on the Access Codes menu to become invulnerable.

Input these in the "Secrets" section, in order to access the levels of Half Life : Blue Shift.