Today is a public holiday in Thailand to mark Visakha Puja Day*, the most important Buddhist holiday. It marks the three most significant dates in the life of the Lord Buddha commemorating the day on which he was born, achieved enlightenment and passed into Nirvana. All three events occurred on the full moon of the sixth lunar month which means that the holiday usually falls in May, but sometimes can be June.
On this day, Thai Buddhists try to uphold the Five Precepts (keeping to the Five Precepts is called Rub Sil). One of the Precepts is not to take intoxicants, so there should be no alcohol taken today which in theory means that many bars and clubs will either be closed or just serving non-alcoholic drinks.
Thai Buddhists visit the temple at dawn and make merit (tam bun) by offering alms to monks or releasing birds from cages. In the evening the temple is again the focus of attention for the candle ceremony known as wian tian (wian=circle; tian=candle). Holding flowers, incense and a lighted candle, Buddhists walk clockwise around the main bot of the temple.
*may also be written as Visaka Bucha or various other similar alternatives.