Tagea would seem to make the most sense. It is the closest, though it is important to point out it is also a nation in itself (via the map), which may not appreciate treasure hunters from Aachen taking its hidden wealth away.
There are several other nearby islands, but I don't think we want to get caught up going too far south, considering how far north the Broken Fingers are.
It also seems we have the ruins of an ancient bridge to navigate before we get there, which could house both hidden treasure and danger in its shadow.
I'm happy to sail wherever, so lets get some more input
