Visakha Bucha Day commemorates three defining events in the life of the Lord Buddha which all occurred on the full-moon day of the sixth lunar month. The Visakha full moon marks the day on which Buddha was born, reached his enlightenment 35 years later and the day he died and entered Nirvana 45 years after that. The photo is the famous Reclining Buddha statue at Wat Pho in Bangkok which depicts the Buddha entering Nirvana.
Most Thai Buddhists will visit their local temple to make merit. Because it’s such an important Buddhist day in Thailand there are also restrictions on alcohol sales which means that some bars and clubs close for the day.
Thanks for useful information from: https://www.thaizer.com/festivals/visakha-bucha-day-in-thailand/