Half-Life 2/Secrets

Look for the Lambda sign (the half-life symbol) this is a clue to some hidden goodies.

Also look out for the G-man, you will see him from time to time on your journey.

whenever there is a breencast up, turn on console and sv_cheats 1, then noclip and find a box that when noclipped into, has a dr breen half body (probably referring to half life)