April
Songkran
The Thai new year water festival. The dates are slightly different depending on the region but generally. 13th, 14th and 15th of April each year
Bangkok:
13th, 14th and 15th of April. Some of the best areas for Songkran in Bangkok are Silom Road video below. Khaosan Road, Soi Cowboy and Nana Plaza (Soi 4 Sukhimvit Road)
Chiang Mai:
13th, 14th and 15th of April. The best place is around the Old City Moat. Everyone around the old city Wall likes to get involved, restaurants, general shops etc. Can not recall anyone charging money for a water refil here in Chiang Mai.
Pattaya:
Pattaya has the longest Songkran in all of Thailand it runs for 1 full week of non stop water fun.
13th, 14th, 15th, 16th, 17th 18th and 19th of April!
Songkran is held only on the last day of Pattaya Songkran the 19th of April
May
Fruit Festival
Central Pattaya
November
Loi Krathong (ลอยกระทง)
When: Each year the date varies as it takes place on the evening of the full moon of the 12th month in the traditional Thai lunar calendar.
What: Loi (ลอย) means “to float”, krathong (กระทง) “a small floating container made of leaves”. Also knows as Lantern Festival.
On the night of the full moon, Thais launch their krathong on a river, canal or a pond, making a wish as they do so. The festival may originate from an ancient ritual paying respect to the water spirits.
Where: All over Thailand