The work opens with a foreword by David 'Zeb' Cook in which he muses on the durability of his invention, the arboleth - a monster with an almost-thirty year history and which features large in this book. A fascinating muse on how the arboleth came to be later, Chapter 1: Lost Cities of Myth and Legend explores the inspirations for this setting. Legends of fantastic civilisations lost to the deeps provide plenty of ideas, after all, as well as a compelling lure for characters looking for somewhere to explore. For that's the intent of this setting: exploration, rather than somewhere to actually live as a denizen of the deeps.
The legendary civilisations of Atlantis, Lemuria and Mu are detailed, along with thought-provoking ideas on how to use them as inspiration for your own sunken empire, before the text launches into the design of a new lost city called Ankeshel for your charaters to research and explore. Ankeshel draws on both real-world myths and the Pathfinder setting, with some Theosophist theories mixed in for good measure, including the concept of vril. The original human inhabitants were taught magic and mathematics by a strange tentacled, 3-eyed amphibious race. Needless to say, it all ended in tears and the city was lost... until recent discoveries began to bring tantalising glimpses of what once was back into general knowledge. Meanwhile a modern settlement has arisen on top of the ruins to provide a base for adventures.
Chapter 2: Pelagic Characters starts with a new race, the Meareans or half-merfolk, ideally suited to underwater exploration and with a few other ideas to make maerean characters predisposed to wish to explore! The discussion moves on to adapting existing classes to better suit such exploits, basing the adaptations on such concepts as modifications due to being raised or living in coastal areas where great familiarity with the sea would be an advantage. There are new clerical domains, for example, and plenty of water-oriented class skills and new underwater feats.
Next, Chapter 3: Aquatic Equipment and Lost Technology is a heady mix of gear you might use exploring under water and goodies that you might find there. Delightful ideas abound: such as using an unseen servant to pump air to your diving suit whilst underwater! The 'ancient technology' is even more fascinating, and the rationale used in its design is discussed, empowering you to come up with more along the same lines. When you are playing a fantasy game anyway, to come up with concepts that will be 'fantastic' to the CHARACTERS rather than the PLAYERS can be quite a challenge, but one that is well met here. This is followed by Chapter 4: Spells and Magic Items. Most of the spells have some aquatic connection, some are to do with glyphs - wound into the ancient writing of the original denizens of Ankeshel is a system of magic glyphs and some astute spell casters may learn the art of their manipulation. The magic items section concentrates on those which survived the fall of the ancient civilisation, with many suggestions as to how to make these as wondrously strange as the lost technology described earlier. How about a shield with magic tentacles mounted on it that reach out to disarm your opponent?
Chapter 5: The Sunken Environment looks beyond the specific challenges to the sheer wonder and strangeness of adventuring underwater. While players might watch the Discovery channel or be SCUBA divers themselves, it is a wholly new environment to their characters. Likely resources available to adventurers are discussed by level, a handy approach both in planning adventures or when planning to undertake them. This moves on to a look at the various environments from coastal zones to deep depths, detailing precisely what you'll find there, challenges and opportunities alike. Next, Chapter 6: Creatures of the Deep provides some interesting new beasties to populate the depths... and a full-blown ecology of arboleths to complete the chapter, and the book.
More than merely presenting a novel adventure setting, this book sets out to equip the GM with the tools to set his own stamp on what could well become memorable adventures, demonstrating how to create a feeling of wonder even amidst what is already a fantastical alternate reality.
[5 of 5 Stars!]