If you fully explored every nook and cranny of Grand Theft Auto III, or even the PSP version of LCS, chances are you know about this already. But in case you don't, there's a perennial secret slipped into each 3D version of Liberty City that's worth taking a look at.
On Staunton Island, there's a walled parking lot at the southwestern corner. Around the entrances on the north side is a staircase that lets you walk along the top of the walls. Climb up, take a right, hop up onto the roof, go straight and drop down into the huge, hidden courtyard.
Poke around, and you'll find a secret message. In GTAIII, it was a big block-print poster that read, "YOU WEREN'T SUPPOSED TO BE ABLE TO GET HERE YOU KNOW." In the PSP LCS, it just said, "Hello again!" This time around, well… see for yourself: