5. Take a Cold Shower or Go Swimming
It may sound obvious, but it's worth saying: If you're hot, cool off your core temperature by immersing yourself in cold water. Unless there's 100% humidity, the evaporation of water off your skin will further cool you once you emerge from the water. For a short cut, use water and ice cubes to keep your wrists cool; since your blood vessels are so close the skin there, you'll feel cooler by applying cold directly to your blood.
Related: Stunning Natural Swimming Pools.