Located underwater, off of the east coast of the State of San Andreas, lies a small circular structure set into the seabed. There is a small rectangular window set into the top of this, which lights up when the player draws near. This is believed to be a reference to a structure called The Hatch from the TV show Lost. In the TV show, The Hatch is a large steel entrance to an underground station. However, this structure was in the jungle and not at the bottom of the sea. The Hatch cannot be opened and its purpose remains unknown. The Hatch is located just outside the kill zone. When approached, the player's submersible will be crushed from the pressure. The player cannot approach it while scuba diving either. The invincibility cheat also gets disabled at this point. Mods that enable to open the Hatch / go inside of it recently surfaced on the internet, but its interior remains inaccessible by normal means.
If the player swims just above the Hatch, a strange tapping noise is clearly audible. The tapping noise has no clear pattern, and many players have hypothesized that the tapping noise was Morse Code, which would possibly reveal a secret message to the player if deciphered. The noise is actually a Tap code, which is a code composed of short taps and pauses similar to Morse Code. The code is deciphered, as "Hey, you never call, how'd you fancy going bowling?" This message is a humorous reference to Roman Bellic, the cousin of Grand Theft Auto IV protagonist Niko Bellic. He frequently calls Niko to engage in friend activities with him at the wrong moments, much to the chagrin of players, making them most of the times not receive his call at all.