In the uderworlf glitch in the Ganton gym, spawn a jetpack and fly up though the missing tiles. Pause, and mark the spot on your map 1 1/2 blocks up from the los santos stadium. spawn a parachute and jump down into the "pit". Skydive to the marked point and there shoud be a remote explosive. Walk in front of it and to the left of it and you should enter a betting place. Exit the betting place and you will be back outside in the real world, but the map is messed up, thinking you to be still 1 1/2 blocks up from the stadium.