The Merikit celebrate with a mummery beside the well at Kithorn, and by a custom known as "burying winter," or "burning the Burnt Man." This is done to help the season turn, because during the longest night of the year, the Merikit fear that it won't.
In Kothifir, the solstice is a big celebration. Kothifirans dress in costumes, masks, and body paint. Trinkets are distributed, and there are bonfires. There's a huge mummery, featuring Winter and the Spring Maid.
↑Honor's Paradox, "Chapter II: Winter Solstice" (Winter 65), I
↑The Sea of Time, "Chapter XIV: Winter Solstice" (Winter 65)
↑Seeker's Mask, "Part VI: Mount Alban", II — " 'the Merikit burn the biggest log they can find, then bury whatever remains of it along with everyone's hearth ashes. "Burying winter," they call it, or "burning the Burnt Man." It's meant to hurry on spring, you see. Then these cinders start to turn up in their fireplaces.' "
↑Honor's Paradox, "Chapter II: Winter Solstice", I — " 'Because it isn't dawn yet, nor may it ever be.' […] The Merikit girl shivered, hugging herself. 'Suppose the sun never rises? Suppose we stay buried in the dark, in winter, forever?' "
↑The Sea of Time, "Chapter XIV: Winter Solstice" — "Many wore elaborate costumes and masks reminiscent of the Old Pantheon gods […] A few had on giant heads that required support or waved oversized hands that tried to swat the children who swarmed around them, jeering. Others, all but naked, were painted red or blue or green, touched here and there with luminous dust from the caves below. […] torches and bonfires, and the windows and balconies above were full of spectators, who threw down trinkets to encourage the capering hoard below."
↑The Sea of Time, "Chapter XIV: Winter Solstice" — "The guilds had built elaborate stages all around the perimeter on which the mummers would play out the evolving story in which spring defeated winter. The first stage, spangled with glittering snow, provided the setting for the Spring Maid’s birth as a golden crocus."