Saving my island idea here as well so I can easily version it.
So the core idea is basically an island that isn’t really an island anymore. It’s more like a shattered atoll — lots of smaller bits of land sitting close together, with narrow channels, reefs, and half-sunken ruins between them.
The important part is that you’re constantly switching between sailing and being on foot. Sail a short distance, dock somewhere kind of awkward, explore, then get back on the boat again. It’s meant to make Sailing feel genuinely useful, not just “teleport but slower”.