The Twin Soul Rocks
by RobinThis canon location has been expanded by Irving Galvez and is detailed in Threshold Magazine 16
I worked in this with cooperation of Irving himself
and some minor changes to the adventure he created were made in mutual agreement.
I changed the orientation of the Dungeon Map (Dark Brown on map, where the underground river is Dark Blue)
I made paths along the rock, which are mostly hidden from viewing them outside the island, leading to the scout towers you described.
I added a simple yet functional alarm system many real world pirates did use (tubes with threads/thin yet sturdy rope within attached to bells in the captain room, and vise-versa)
As you see the 4 scout towers as discribed in the adventure are marked as underground towers which in fact they are, albeit not real towers, but only hidden lookouts.
These lookouts have a rope/bell system to the captains cave through plant tubes(bamboo possible) to prevent birds disturbing them.
In the adventure Irving did suggest the mountain is a volcano and the tunnels correspondingly.
Studying the area intensely I think this is a wrong suggestion.
The overall region may have several volcanic locations, yet when looking at the rock themselves, the valley--now channel--is geologically more suited for a former glacier.
Looking at the mountain before 1700BC, this is more than logical, the sinking of the continent, lifted the glacier without damaging the underground too much. while underneath its frozen muddy morene/basement remained underground firmly attached to the rocks and would slowly thaw, and the water would thus create the tunnels, and especially the tidal cave. A volcano could never have done this.
The sunken ruins underwater are all ancient Taymoran settlements dating before the 1700BC disaster. This includes the tower, and some unidentified ruins. large squids (up to 20 feet) often took residence in these hunting for shells, crabs, and remains as being scavengers. They will not attack vessels, but will defend intrusion in their lairs.
The crystals growing on the Island are not discovered or researched and any magical abilities they might give is as of yet undetermined.
The Rock islands are further as Irving revealed in his adventure, mostly occupied by birds, some seals, crabs, and have no real predators dangerous to the passing vessels. Once in a while a Large Roc might rest or feed here temporarily, yet this one is fishimg for whales several miles away from the island, and has no nesting interst here (nor location) and is uninterested in the vessels. Some feathers can be retrieved here for the spellcasters interested in components, or whale remnants on the rocks, further devoured and spread by the local birds (mostly seaguls, and alike) and the weather.
In the water are living mostly Mako Sharks (Stats found here; page 312 )which can be dangerous.
Some Merrows and Sharkin hunt here regularly, and these can be encountered if going underwater only. They refrain themselves to contact surface dwellers if possible.