The heaviest of the Westvleteren beers, the 12 is a quadrupel style beer, which can be recognized by its yellow cap. Like the other Westvleteren beers, the bottle does not have a label, and the cap therefore has all the required information.
The Westvleteren 12 has always been rated high on beer reviews, and is by some considered to be the best beer in the world.
Just as the other Westvleteren beers, it can only legally be purchased at the monastery (on appointment) or in the bar across the street. However, it often finds its way on the grey market where it's sold at high prices.