With Ayla away, Kino is acting as the village chief.

Kino: Lavos fell.
Dinomen destroyed, good.
But getting cold since then...
No can hunt much...
But Kino not lose!
Ayla no need worry.
Leave to Kino.

KINO: Lavos fall.
Reptites gone. Good!
But get cold now.
Hunting bad...
But Kino not give up!
Ayla no worry, leave to Kino!

The Larubans have taken refuge at the Ioka meeting site.

Iokans and Larubans both seem concerned about recent changes in the weather.

And then there's this line that some link to Chrono Cross's Frozen Flame, though I suspect it's just a vague clue to getting the Silver Stone.

It's a quick trip back to Mystery Mountain and the Gate within, especially with fewer monsters.

Things are the same as ever, except that the links to the sealed Gate are missing.

Old Man: Oh? So you're back here after
seeing that land of magic...
As the pillar of light has been sealed,
you need wings that can freely come
and go through time.
Wings that Cross Time...
There was a man researching such a thing.
Though I'm afraid he's lost a bit of his sanity,
with being too immersed in his research...

Time to check out all those sealed doors. "Sealed Door" plays after the door opens in response to the pendant. In this room are chests containing a High Ether, a Captivating Bra, and Echigoya's Wallet.

There's a man here who wasn't before, and a seedling plant.

The door is where it has been. This one contains a Magic Capsule, a High Ether, and a Gold Pierce.

The party stops by to see how Don and the others are doing.

Don: Oh, it's you guys! Look!
Those seeds have sprouted!

The sealed door in the basement opens now, yielding a Power Capsule, a Robe of Light, an Elixir, a Hit Ring, and a Gold Earring.

Crono and the others have to cross the underground waterway to get here. It's a lot faster if the bridges are already in place from before, but if not, everything there is a pushover anyway by now, so it's no problem. "Sealed Door" plays in the dome. A Nu is sleeping just inside.

Enigmatic Object: I WAS AT LONG LAST SLEEPING
PLEASANTLY, SO PLEASE DO NOT WAKE ME.

Anyway, the sealed door is in the back, just like before. It opens in response to the pendant. Soon after Crono enters the sealed room, several sparkling somethings appear on the ground.

The sparkles seem to contain some kind of recording, because each gives a message.

Crono opens the inner door that is just ahead. The room inside is unusually clean for this era, and contains a machine that's a bit larger than a car.

Lucca: This is the last invention of Gasch,
the Philosopher of Reason...

Robo: THIS is the Wings that Cross Time,
that WAS in the record earlier...

Ayla: !!
This...

Marle: This is... awesome...
But which side would the front be...?

As the party approaches the doorway, the Nu walks in, pushing a platform with three seats.

Enigmatic Object: You seem surprised.
It's me...
That's right, Gasch.
I copied my brain into this object.
Does it meet your liking?
There is something that I must
explain to you.
That is, how to go to another era.
The time gauge appears by using
the green button.
Choose the era you want to go to
with L and R.
Ah! That's right!
Before leaving, why not try giving...

Remember that on a Japanese Super Famicom, the buttons are color-coded, with the Y button being green. For no apparent reason, the buttons on the US SNES were changed to two dull shades of purple. This is important because there's no opportunity to press the Y button at this point. While that does eventually become the time travel button, for now you just get in and go, so the "green button" sounds like it's referring to something on the machine's control panel, with no connection to the player's gamepad.

The Nu falls asleep in the middle of talking. Crono wakes it back up.

Gasch: Why not try giving this time
machine a name?

The default name is シルバード , which appears to be "silver" and "bird" run together, so I'm rendering it as Sylbird. It's "Epoch" in the NA version.

Check in the previous room at this point or later to find a Magic Capsule.

Crono and the others get in the seats, which raise into the machine.

The internal storyline progression tracking variable is now 0xAE.

Choose 作動 (operate) to make the time gauge pop up. The Sylbird's time gauge has options for 65 million B.C., 12,000 B.C., A.D. 600, A.D. 1000, A.D. 1999, and A.D. 2300, and going off the top end of the gauge leads to the Farthest Reaches of Time. Let's head there for now... Crono hits the button, and the room distorts around the machine and vanishes with a loud cracking noise. The Sylbird passes through what looks a lot like a river of flame...

Robo: Energy such as I HAVE never seen!
As though it HAS amplified the power of
the human spirit to a terrifying extent...!!

Robo: There WAS never any such
thing as a timespace vehicle even
in MY era...!

Ayla: This guy great!
This guy strong!!!

The Sylbird reappears in the misty nothingness with a similar cracking sound, followed by what sounds like a cooldown. Everyone jumps out, landing on the platform where the old man is. Speaking of him...

Old Man: I see, so that man completed it.
The Wings that Cross Time...
in exchange for his life...
Why not try flying on those Wings now?
Yes, to that ancient land of magic.

Besides the doors in the future, there are many sealed chests in the Modern Age and Middle Ages that the pendant can open now. Those that are only found in one age or the other open immediately. Chests that appear in both will give the option of leaving them closed, if touched in the past. Why? Well, touching the chests in the past but not removing the items inside causes a reaction that leads to better items in the chests in the Modern Age, much better in some cases.

In particular, make sure to use this trick to get the White and Black Plate in the Palepoli elder's house, the Red Plate in Guardia Castle, and the Blue Plate at the inn in Truce Village. After getting the upgraded chests in the Modern Age, head back to the past to grab the originals (White, Black, Red, and Blue Mail). You get to keep both even though you might think that would cause a time paradox. Apparently time traveler's immunity applies to your inventory as well as your characters. Also, Taban will now give Lucca the Taban Suit, with his usual speech.

The Sylbird always appears in the same location, more or less centered on the map, regardless of the era. After collecting treasure and stocking up on supplies, Crono takes the Sylbird back to the time of the ancient kingdom. Unfortunately, the transporter to the floating islands is offline. With a bit of exploring, the party finds another cave...

The ladder to enter had been retracted on earlier visits, making the village inaccessible before now.

"Silent Light" plays. The cave has been converted into a primitive, but livable, village. Amusingly, they have better equipment for sale than the shops in Zeal do, including a sword for Frog that has even higher attack power than the Grandleon.

Elder: I heard from the Philosophers that
lord Jyaki hides an incredible magical
power that surpasses even lady Sara.
However, he hates that power, which drives the
queen mad and torments lady Sara, and along
with his heart... he has shut that power away.

Ick. Horrible meaning distortion. Blech. He's so against Lavos power that he's rejected his own magic.

A Mud-Eater (Beast), as it turns out, is a large, horned beast. It has somewhat elevated physical defense, and starts with low attack power, but its attack rises every time you hit it with anything. Use combo skills for more damage in fewer attacks. Ayla can and should steal from them, because the Rainbow Helmet they carry has high defense, halves Aether damage, and can't be found anywhere else. The creatures will also reappear if you leave the cave and return, and the village has an inn that doesn't charge anything, so feel free to stock up.

At the far end of the cave, a brown goblin, a red Mud-Eater, and a blue Mud-Eater guard a large chain that continues up out of sight.

Upon encountering the goblin, the internal storyline progression tracking variable becomes 0xB4, starting the next chapter.

Okay, so maybe visiting the ruined future has given the people a bit of hope, but unfortunately, the situation remains exceedingly bleak. Of course, the plan is to stop Lavos before the devastation occurs and avert this future entirely. Charging sealed chests in the Middle Ages has an effect on the Modern Age, but it's limited to the chest contents, and no one else knows how to open the things anyway, so it doesn't really qualify as having any historical impact. But who knows, maybe this whole philosopher rescue mission will go differently.