I took the squid carving and put it in the door (after moving it around to face the right way, which you have to do with all the boss keys). After walking through the door, large tentacles started piercing the ship. The ship was under attack. I had to use my charged-up sword to slice the tentacles and make my way to the deck of the ship.
Once outside, the boss revealed himself: Tentalus.
I gave him a haircut so everyone could see his beautiful face.
After defeating him, I struck the Quake logo and the blue flame erupted and went into my sword.
It gave Smurf-Fi additional dowsing abilities. I can now dowse for more things, including treasure. Smurf-Fi told me I need to return to the Isle of Songs so I can learn a new song on my harp. But I wasn’t quite ready for that. First, I went back to the Sandship (it’s repaired already, imagine that) to get a treasure chest that I didn’t get to before. It contained a piece of heart.
I then returned to the sky. I checked out one of those marks on my map where striking those stones on the surface opens something new in the sky. But when I got there, there were treasure chests, but I can’t open them. I’m guessing I need something else before they will open, but I’m not sure.
Anyway, I saw another strange island and landed there. A person told me they lost their party wheel, which fell beneath the clouds. Apparently this is a side quest. Smurf-Fi added the party wheel as a dowsing target and told me it would be in the desert. I didn’t go looking for it, but I may do that soon.
I then went on to the Isle of Songs and learned my new song, Din’s Power. It will open up a trial at Eldin Volcano. I’ll save that for another day.
I went back to Skyloft and did some shopping. I’m also noticing a lot of people with thought bubbles, which means they need help. So I’m seeing lots of opportunities for side quests. I do like to take a little break from battle after completing a dungeon, so next time I may just try to help some of these people out, and hopefully score some good rewards in the process.