Seekers of the Misty Isle
This well-made tome is always of small size, typically no more than 12 inches tall, 8 inches wide, and 1 inch thick.
All such books are durable, waterproof, bound with iron overlaid with silver, and locked.
A wizard can fill the 1,000 pages of a blessed book with spells without paying the 100 gp per page material cost. This book is never found as randomly generated treasure with spells already inscribed in it.