Get in any land or air vehicle and drive or fly to the abandoned air field in the region of Las Venturas. To the south from here, there is a little area that is a "no fly zone". If flown over, a mysterious five star wanted level will appear. This is because the area is a government agency secret base that holds several heavy and speedy army vehicles. You can also find this area in the middle part of the region of Las Venturas on the map included with the game.