Congratulations! Cool find! I've often wondered about what's under the island ruins because they hint at something don't they, but my sims have never had an adventure there either ... and they've had the axe with them before. I suppose if you had a sim with one of the adventurer life time wants and focused on the World Adventures for long enough you'd end up finding something under everywhere. There's probably something under practically every square, except for some residential houses - there's some with adventure tombs underneath, they're annoying to access aren't they and sometimes it seems having the inappropriate happiness reward doesn't work.
Anyway, be swimming in sims there eh.
