Songkran is my favourite festival… if you are ever in South East Asia around April I suggest you try and be in Thailand for Songkran.
Traditionally Songkran was a gentle splashing of water on the shoulder of the elderly folk in the village to show them respect and to wish them good luck. Somehow over time this has morphed into a 3 or 4 day nationwide water fight! It is totally crazy and oooh so much fun. Songkran comes at the hottest time of the year and the water is usually well received (although you do get a bit fed up with being constantly wet on the 3rd day).
Chiang Mai is a great place to spend Songkran and see a bit of tradition as well as a lot of craziness. In Chiang Mai they have a big parade of the Buddha statues from the important temples, the people in the street then toss water on all the Buddhas to help cleanse them and bring good luck.
Here are some photos of our Songkran in Chiang Mai: