Maybe there's a note!
There is!
"Dear Fellow,
It appears you are stuck on our island. Since you have surely forgotten about what happened:
You arrived by boat for my wonderful mansion party. But it crashed and you nearly died. Now you have set camp and you need to find your way to the party.
We can't help you, however.
You're on the opposite end of the huge island.
But either way, if and when you get here (if you even see this message),
Please come and we have a surprise for your troubles!