Belleteyn or Beltane, sometimes known as "May Day", "May Night" or "Blossoming", takes place on the night of May Eve, the night of April 30 into May 1. It is a fertility festival beginning at dusk on the 30th and continuing until the dawn of the 1st. It is also a traditional time to begin (or end) relationships of a physical nature. Food, drink and love are the order of the evening making this celebration a time of many marriages. Bonfires abound, and revellers are encouraged to jump the flames for luck and their own fertility.
- Belleteyn is analogous to the real-world celtic holiday of Beltane (anglicised form of the insular celtic "Bhealtaine" and continental celtic "Belotenia"), which is still celebrated to this day.
- In The Last Wish, it's stated Yennefer was born on Belleteyn, and Geralt calculated that Ciri was also born near the festival.
- Geralt meets Yennefer at a Belleteyn celebration in Sword of Destiny.