Longshore Skull (achievement)

Longshore Skull is an achievement in Halo 3 and Halo: The Master Chief Collection. It is unlocked by finding the hidden skull on the map Longshore.

The achievement is worth 25 Gamerscore in the original game and 5 Gamerscore in The Master Chief Collection.

Location
The skull is located behind the air ducts left of the garage door that says "do not block", in the left upper corner of the map (when facing away from the fish taco shop). To grab it, enter monitor mode and fly behind the air ducts, then go back to normal mode and pick up the skull.