You are given it by the girl at the mueseum!
If your talking about Counterfeit Island then you get the key and go back to the museum on Counterfeit Island
You use it.
Early Poptropica.
The key fits the Inspector's cottage in the Countryside.
In the supply room
you get in the boat and sink
It will.
blah blah blah
skrow you
You now have a key that fits a lock on Counterfeit Island, and you haven't found a key to the lock on the Inspector's house, so...
First go to skullduggery island,take your ship to a island called Keys World island and you will find the key of the chest on counterfeit island!;)
There is no key. Go upstairs to find the painting.