From the introduction:
Frost borders the dawn-lit windows of the lively tavern called The Loamy Garden. The patrons are enjoying the tavern’s specialty on this cold Midwinter morning—a hot mulled cider brewed with juniper and cinnamon. Aromatic wisps of steam curl lazily up from their mugs, filling the room with a sweet, peppery fragrance. While it is dreadfully cold outside, the fire in the hearth burns warm and bright, casting a pleasant glow about the room.
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Bastion of the Frost Lord is designed to be completed in about 4-8 hours of play. The combat encounters have been calculated to present a tough challenge to four adventurers of 5th level—that is, the target average party level (APL) is 5. Information is supplied in the text explaining how to scale the encounters for APL 6 through 10.