Sri Lanka observes poya days — full moon holidays — every month. On poya days many shops and restaurants close, and the sale of alcohol is restricted. They are peaceful, slightly strange days to be a tourist, and they punctuate the calendar. The most important poya days are Vesak and Poson.
Vesak (May full moon) celebrates the birth, enlightenment, and death of the Buddha. Streets are hung with elaborate paper lanterns and pandols — large illuminated displays depicting scenes from the Buddha's life. Colombo and Kandy light up spectacularly. The full moon night is the peak, and people stay out late watching the displays and visiting temples.
Poson (June full moon) marks the arrival of Buddhism in Sri Lanka in the 3rd century BC. The centre of the celebrations is Mihintale, the hill where the Indian monk Mahinda met the Sinhalese king and converted him. Vast numbers of white-clad pilgrims climb the steps at night. If you can get to Anuradhapura and Mihintale for Poson, it is a memorable experience.
Esala Perahera is the grandest festival in Sri Lanka — a ten-night procession in Kandy during the Esala full moon (usually July or August). Dozens of elaborately decorated elephants parade through the city, along with dancers, drummers, fire-jugglers, and acrobats. The final night, Randoli Perahera, is the most spectacular. The city fills up; accommodation in Kandy and the surrounding area books out weeks in advance. Going without a plan for where to sleep is a bad idea.
Sinhala and Tamil New Year (April 13–14) is the biggest secular holiday of the year for both communities. It celebrates the traditional new year and the end of the harvest season. Businesses close, families gather, and traditional games and rituals are observed — the exact time of the new year is astrologically determined and announced each year. Travel on April 13 is complicated by road and rail congestion.
Nallur Festival in Jaffna, in the north, is one of the great Hindu festivals of Sri Lanka — 25 days of rituals and processions at the Nallur Kandaswamy Kovil in July and August. Far fewer foreign tourists make the effort to get to Jaffna, which means you see it in a more genuine context than most.