Instructions
Find the large building east of the Las Venturas Transfenders. This may take a little driving around, but visiting the restricted area is well worth it.
Move to the south side of the building and locate the entrance. You'll notice that the doors are not solid.
Burn a jetpack by hitting the following sequence on your controller. (Left, Right, L1, L2, R1, R2, Up, Down, Left, Right.) Then move into the entrance, which will bring you to a place called Blue Hell.
Stay low and fly until you reach the restricted area. If for some reason a "wanted" warning flashes, simply ignore it. You can't be found inside of Blue Hell.
Travel through the labs and until you discover a corridor that has a grated floor.
Locate the atrium within this corridor. Then move to a tiny entrance, which will lead to a water way below the grated floor.
Rise into the labs by moving through the ceiling directly above the grated opening.
Explore to your little heart's content. You have found the Area 69 labs, now exploit the video game and see what you find.