Finally, I figured out that I needed to find Jabu Jabu in the sea. Some time jumping later, to avoid rocks and things that existed in different places in different times, and I found the Zora Village under the sea. Several sub-quests needed to be performed before entering Jabu Jabu’s belly, however.
Firstly, the Zora King is sick (in the past) and dead (in the present). Nipping off to find Syrup the witch, I bought some Magic Potion which brought him back from the brink. Then I needed to clean the sea for him, which the Fairy Queen could do. At least, she could if she hadn’t been turned into an Octorok. Fairy Powder would turn her back, and that is kept in the local Library. Unfortunately, the library doesn’t have the required book to let me access it. Taking a book from the present to the past (another paradoxical time loop thing, it seems) allows me to get the Powder, once I completed an invisible floor puzzle.
Finally, with the Queen back to normal, the sea clean, and the King happy, I could go into Jabu Jabu’s belly – Dungeon 7.
This dungeon was on three floors, which could be flooded to different levels by use of switches. Different parts of each floor become accessible depending on whether they’re flooded or not. So it was like some kind of huge puzzle. The mid-boss was alarmingly simple – it was a puffer fish that bounced around the screen. Shoot it with seeds, and it deflates, allowing you to hit it with your sword. And that’s it.
The weapon picked up here was an upgraded Switch Hook, which lets me swap places with items further away. And yes, you need it for the end boss, who once again was very easy to kill.
Once out of the dungeon, I learn the Black Tower is complete, and people are being turned to stone. The tree has no idea where the final Essence of Time is, so neither do I. Better ask around then, I think.