Each 15th tends to be a market/fair day in most cities
15 Longday and 15 Longnight are the summer and winter solstices. The summer is marked with public celebrations while the the winter is marked with more private (or at least, only community-based) celebrations involving lights.
15 Growth and 15 Chillwind are the spring and autumn equinoxes
A shower of meteorites tends to occur each 22-25 of Starfall. It is seen particularly well in Tarsas and the other southern lands.
1 Awakening is a day filled with feasting and with a fair to celebrate the new year and seeing friends and neighbors
On or near 1 Harvest is generally the day of special Harvest fairs in most lands