The Verbeeg Valley

From publisher blurb:

This "encounter" is designed for you, the Dungeon Master, to conduct at any point between the series of modules within this Super Adventure. You can run it after the G4, the G6 or the G8 (running it between the G5&6 or G7&8 is problematic, for the first one in those pairs leads directly to the next in sequence, with little room or reason for the party to divert to this). That being said, you can even run this before the Super Module begins, or after the last installment.