Take a look at the map. To the left is a big lake called 'Largoe Rodrigo 
de Freitas'. Drive to the top, right corner of the lake. There you will 
find a building. Go around the back of that building. On the right corner 
of the building is a door, just press it and you have unlocked the cheat. 
You should see a garage with barbed wire just to the right of this building 
if you are in the right place.