On the morning of the first day of work for new Letter Bee, Lag Seeing, and his dingo Niche, the sub-master of the Bee-Hive, Aria Link, stops by Sylvette's house where Lag is now living.  She shows him to a place known as the Hill of Prayer, where everything with Gauche had its beginnings.
The place in Yuusari Central where you can feel closest to the light of the artificial sun.