A holiday that’s now a day of celebration of midsummer which originally used to be a celebration of Helios’ sovereign power over the Sun where he destroyed an enemy by focusing the entire light of the Sun on them and immolating them (the latter obviously all entirely forgotten now.)
On the evening of midsummer fires are lit everywhere possible and kept burning bright all night in an attempt to “extend” the longest day of the year even longer. In Helios' time this was to guide Helios's chariot. The forgotten God of the Sun has the heaviest burden on the longest day and the peoples of Thylea build bonfires to the west of their households/settlements to make sure he does not crash from exhaustion before over the horizon.