stone tentacle key. What can this open?

It seemed to be worthless on the island. Where then does it go?

You need it for the most profitable path on the island, taking your net to the well. You will also need it for the Heart’s Desire Ambition.
edited by Nigel Overstreet on 10/5/2012

Additionally, Failbetter has said that the Stone Tentacle key will be needed for each ambition. Hearts’ Desire just needs it soonest.

I say with certainty that if one is pursuing a nemesis, they will require the key when they go to the Iron Republic.

Well, technically you don’t need it for Heart’s Desire.[color=#ffffff] I offered my dreams instead[/color].

Well, unfortunately back when I was starting I just clicked things to see what would happen. I had no idea that I was starting my ambition when I picked ‘hearts desire’. So even though Nemisis or bagging a legend sounds more interesting, this is what I have. Is it possible to switch or finish one then do the others? Or maybe are there more than one tentacle key? I’m at the point now that I can trade the key to the cheery gentleman… it seems strange to me that the key isn’t actually going to open anything, just given away as a trinket.

Currently, none of the ambitions have finished, so you’ll end up stuck at the content boundary. You can spend 50 fate/nex on tea leaves for switching, however.
Additionally, you can regain the key after you’ve given it to the gentleman with another run of Hunter’s Keep/Christmas presents.
The key might at some point open a door, but so far we haven’t found it.