http://www.ratebeer.com/beer/westvleteren-abt-12/4934/http://www.westvleteren.dk/Westvleteren
Westvleteren has the smallest output of the Trappist breweries. Basically, you have to go to the Abbey or the Café In de Vrede to buy their beers.
The Abbey has been brewing beers since 1839. Between 1946 and 1992, the brewery Sint-Bernardus in Watou was allowed to brew their beers under licence. Their Sint-Sixtus Abt, at 12%, was my first encounter with beers from Westvleteren, back in 1987.
Westvleteren is actually producing 3 marvellous beers: the Blond (green cap), since 1999, which then replaced the 6 Special (red cap, 6.2%) and the 4 Double (green cap, 3.5%); the Extra 8 (blue cap) and the Abt 12 (yellow cap). The alcohol % of this last beer was recently reduced from 10.8 to 10.2.