The only huge international festival I've been to was the running of the bulls in Pamplona, Spain. I was only seventeen and my buddy and I were stuck on the French/Spanish border, waiting for a train. Some Canadian backpackers suggested that we go to Pamplona since it was supposed to get to our station before the train to Madrid (our original destination), so we did. Although I was plastered (it didn't take much to get me drunk at that age), I still remember a lot of details very vividly.
If I had a choice of any festival in the world that I could attend, it would be Holi in India. Check it out:
http://4.bp.blogspot.com/-FVdyp6iyMr...ia33545451.png