Westvleteren

I've driven to St. Sixtus. It isn't easy to find. The abbey sits deep within the surrounding pastures on a very narrow back road. You can't visit the abbey itself, but they run a guesthouse where you can purchase food and small amounts of beer. If you want to buy more, you must make a prior appointment to pick up your order at a drive-through window.

Technically Westvleteren is only available from the abbey, (except for a limited release in the US a couple years ago) but a number of people report being able to buy bottles in well stocked beer stores in Belgium. You may just have to poke around.

We found it in a beer store in the centre of Bruges just off of the main square - sorry I can't remember the name of the store or the street. I think if you look around in Bruges for large beer specialty stores, they may have some.