Raiders of the Black Ice
As Spriggy examines the humanoid form, you remember old references to the Nuatian empire, and their advanced magic (for humans). It seems this thing is a form of magically powered construct. You can just spot the ancient crystal that could move it... though it seems to be out of energy.
Interrogating confirms that it was once a 'living' creature, able to talk and tell them of the ancient treasures and fortune of the Nuatian Califate. They built this fortress as a way to protect this heritage of old, as well as a safe base to raid the warmer climes. From your discussion, it's clear there are no frost folks reinforcement coming, and that causing severe damage to the fortress will stop their raids in the area for a long time.
Drake comes back soon enough, and you're able to rest, and help the prisoners recover. While eating, you decide what to do with the frozen construct, as well as the way to bring down the place.
Now's a good time for the End of Session, since the rest is pretty much just an epilogue.
So, for all you've accomplished and learned, give yourselves an extra 6 xp for learning about the world, defeating significant opponents, earning a memorable treasure (not just the token, but also the construct, sort of), and for playing your alignment.
You can also add bonds to your character, if you want to.
Once that's done, feel free to write your final reaction before returning to the guild, then I'll wrap up this adventure.