The answer to “what’s in the hole” is a series of rooms connected by teleporters. In each one, a purple pillar takes you to a small segment of an earlier level with some Heartless to fight, representive of that level, and a chest tucked away somewhere.

After grabbing an item from each of these levels and sorta recapping the game, we come to a flashback room we’ve not scene, with a strange machine.

A large glass sphere containing colourful gases, with complex machinery in front of it, showing keyhole iconography.

It’s definitely very reminiscent of the machinery in Hollow Bastion. Perhaps this is what Ansem used at the start of his evil deeds?

We get some poetries when we examine it.

“Ones born of the heart and darkness, devoid of hearts, ravage all worlds and bring desolation.
Seize all hearts and consummate the great heart. All hearts to become one, one heart to encompass all.
Realise the destiny: the realm of Kingdom Hearts. The great darkness sealed within the great heart.
Progeny of darkness, come back to the eternal darkness.
For the heart of light shall unseal the path.
Seven hearts, one keyhole, one key to the door. The door of darkness, tied by two keys.
The door of darkness to seal the light. None shall pass but shadows, returning to the darkness.
Ones born of the heart and darkness, hunger for every heart until the dark door opens.”

Hmm. So the Heartless want to achieve some kind of Instrumentality type deal? This is all quite cryptic. I note mention of ‘two keys’. Is one of them Riku/Ansem’s keyblade, or one we’ve yet to encounter? Also: title drop.

The time portal turns into a big hole. In we go!

Sora leaping into a large blue portal surrounded by spiky stalagmites.

Inside we find a really big Heartless with big dragon/bat wings. Also we can fly.

Sora flying near a huge black gargoyle-like creature.

Unfortunately for the big demon, it has a severe weakness to being hit in the face repeatedly.

We get the ability to fly faster. Handy!

The next rooms are a kind of diorama of some ruined buildings overrun with thorns.

Then we get to a green room. A Large Friend needs a petting. Then a door starts falling apart while Heartless spawn. That’s probably bad.

Sora on a green floor facing a collapsing, Heartless-symbol portal door.

After fighting many waves of Heartless (mostly the dark ‘Pureblood’ ones, but with the cool four-winged angel jar ones holding up the ‘Emblem’ side), that door breaks apart. We find… another door.

Sora facing an ornately decorated double door, this one with more ordinary handles.

There’s also a save point, called ‘final rest’, which is pretty damn ominous.

I’m not sure if I’ll be able to keep playing after finishing this section, so I’m going to see if I can do the remaining crafting and get the Best Keyblade. And maybe try those two remaining side bosses.