Aeolius
Adventurer
Felon said:But now I have to take the bait. How the heck does water qualify as having "the largest appeal to the masses"? A party trekking through desert or tundra has a certain heroic appeal to it. I can paint a cool picture of that in my mind. But a party trekking across an ocean floor with schools of fish swimming around them and checking their watches every few minutes to see if it's time to take another swig of their water-breathing potions? That just strikes me as an absurd visual. I don't see that as having the greatest mass appeal. Water is an obstacle that separates point A from point B. Sure, your ship can attacked by krakkens and pirates in transit, but that alone doesn't merit an entire book IMO.
If I take the bait, does that make you a troll..err...scrag..gotta think aquatic

The sea represents a mystery, a vast unknown in which to explore and adventure. While its lure may not appeal to everyone, I for one have always been fascinated by the citizens of the ocean.
Take a trip to your local public aquarium or pet store featuring a selection of saltwater tanks. Watch the inhabitants in each aquarium interact with each other. Carefully map the contours of the sponge-encrusted liverock. The variety of life in a simple reef tank is astounding.
Tune into the Discovery Channel when they are showing the "Blue Planet" series or explore the various undersea-themed sections on their website. Look over a few websites that sell saltwater fish, to sample a fraction of the variety seen in the wild.
Start thinking of the ocean floor as more than just dirt. Envision sea grasslands, brambles of living sea stars, or a jungle of sargassum seaweed. Or perhaps a sea urchin barren or dead coral desert would be more to your liking. Then there are jungles of kelp and tangles of mangrove roots in the shallows. Dive a bit deeper to explore hydrothermal vents and cold seeps, undersea lakes of highly salted waters. Add to that the inevitable sunken treasure fleet or ruins of an ancient city thrust to the ocean floor amidst a volcanic eruption.
Imagine how the environment differs, beneath the surface of the sea. Visibility is a constant concern. Enemies can approach from above and below. Communication, combat, and even something as simple as swallowing a potion or scribing a page in a spellbook must be reconsidered.
Some links, to get you started:
An online reseller of tropical fish:
http://www.liveaquaria.com/
Discovery Channel's "Blue Planet" pages:
http://dsc.discovery.com/convergence/blueplanet/blueplanet.html