Drive in and down, ignoring the left turns. Keep driving to the end, then turn right and follow it down, making continuous left turns. When you get to the bottom, turn left again then right, and left once more. Follow that tunnel down to the end to find the secret car on a risen platform. You will see the switch on the right of the platform, on the wall.
Secret car Take the first right turn and follow it down.
Turn left to go to the Tropicana area. Turn right at the second street, then take the first left turn. Look left to see a gate and a building. Follow that building with the four cones in front of it. At the end of the building is an opened gate.