a matriarchy where women are the rulers and warriors and priests; a PC party of mostly men might have a tough time making progress with trade, adventuring etc. here
an abandoned mining site - decaying tools and implements, and valuable but unrefined ore which would be heavy and difficult to transport to another place. The site may have been abandoned due to the mines reaching some strange monster in the ground such as a xorn, or an adjoining umber hulk lair
an evil cult on its own island with prisoners; perhaps one prisoner might help the party or another might be worth a valuable ransom if brought home
an underwater wizard's citadel - all kinds of possibilities and dangers here including water breathing ability long enough to get there, sea animal servants, treasures and perhaps a great magical item like an Apparatus of Kwalish - in fact the climax here might be the party in one Apparatus of Kwalish dueling with the wizard in another
caver slavers - an evil group of slavers operating out of a cave hideaway, preying on ships and coastal towns; perhaps the prince of a nearby island state would commission the party to put them out of business
a small druidic civilization on a remote island, perhaps with some badly needed information that would enable the party to locate another island or solve part of an adventure
a very militaristic culture centered around a warlike navy, perhaps similar to Japan in World War II in that the military leadership runs the show and seeks to conquer and enslave neighboring cultures for their own material benefit, with little respect for other cultures
peaceful sea nomads who live on giant, ancient rafts, trade odd items that they obtain from oceanic races and distant cultures, speak their own language, have their own odd, sea-oriented magic spells and items
The Hole in the Sea - a wide, strange tunnel that opens in the sea's surface; few have ventured into it and even fewer have returned. Those who have returned brought back several different stories, including weird, faraway civilizations (perhaps on the other side of the planet, or on other planes) and a realm far under the sea where humans can breathe without any magic or equipment and can interact with strange sea races and creatures
an island where the culture, religion and society revolve around gaming and gambling of all sorts, with racecourses and casinos of all types to be found everywhere
Maze Island, in which the entire surface - and much of the area beneath it - is a massive maze cut into solid rock, leading to villages, gardens, fertile fields, jungles. If you take a wrong turn you might end up in dangerous places like burial areas filled with nocturnal lycanthropes, deserted areas filled with rotting carcasses and disease, strange hermits or wizards who have hewn their own shelters or libraries into the rock, or faraway and abandoned areas where there is no food or water
An island whose culture is devoted to raising and smoking marijuana. Seriously, this could be a good and trying adventure. These peaceful and generous stoners do not have many physical resources or items to trade besides their huge surplus marijuana crops (for which there may be a very profitable, though illegal, demand in some other island cultures) but if players spend enough time there they will learn that these people have much in the way of strange druidic tradition and spellcasting and a great deal of magical knowledge, largely taken for granted. Weird, minor magical items are common, as are strange and esoteric spells. While these people are very pleasant, they are not very interested in trading; they would rather just smoke marijuana. They can easily be interested, though, with such items as unusual foodstuffs or kaleidoscopes, or unusual artwork or even storytellers whose art they find interesting and engaging.
A culture where the people worship their own body functions to the extreme and seek to have diarrhea and related conditions as often and as strongly as possible. This could lead to a lot of very difficult but amusing situations for the party. In this society it is considered to be very rude to eat in front of people or in social settings, but reliving one's colon or bladder is a social event - the reverse of how eating and going to the bathroom are in most cultures. People eat in small, secluded rooms; instead of shared dining areas they have large multi-person toilet areas where social events are held. Food and water supplies there will leave PCs dangerously ill for days. It would be an amusing but unpleasant place for PCs, but they might obtain spells or items that discomfort or disable enemies with sudden bursts of diarrhea at bad moments. They also might find that mundane commodities such as clay (for making toilets or tile) are rare and desired there, while items coveted elsewhere like gold and silver are discarded (because they make for cold, uncomfortable toilet seats). In fact, gold and silver and jewels might be commonly discarded into the sewers, by children in particular, and one adventure might involve PCs trying to figure out how to retreive gold and jewels from the disgusting, disease and creature ridden sewers - a place that locals hold taboo and that cannot be entered without severe punishment if one is caught.
You'll have to tell me how it goes if you use it.
