This is a fun even taking place in Pajottenland, just outside of Brussels. I went to the last one in 2009 and it was a blast. This year there are 9 lambic breweries/blenders taking part. You can book a seat on a bus that will take you to a certain selection of them, depending on the bus you choose. Let me know if you think you might be in the 'hood on May 1 and I’ll book bus tickets when they become available.
Here’s the website:
http://www.geuzeinfo.com/index.php/Toer-de-Geuze