At the start of the game drive north to Bohan, the island where you get a safehouse after your first one is burned down. At the very northern most road there is a point where the subway train tracks go from an elevated line to underground. Drive a car from the road onto the tracks and head into the tunnel. Eventually you'll cross the river and end up on the locked island of Algonquin and receive 6 stars. Stay in the tunnel for 5 minutes and you'll get the achievement.