For an instant, he goes blind.
Then the strangeness fades - filtered, somehow, into normalcy that his mind can accept.
He's no longer in his Work Room.
He's...somewhere else. Some plane that he doesn't recognize, a churning chaos of half-formed matter and roiling energy. But there is a firmament beneath his feet, a platform of something that holds its shape.
The Gate is behind him. He can feel it, the anchor to his starting point.
Leareth takes a deep breath, and begins exploring this new world.

....

This is not what he expected! Leareth is confused. 

It's - almost like the Void, when he projected his mind there to build his immortality mechanism. But it's very clearly not the Void, which would be incapable of providing a solid surface to stand on. (Or any structures at all, save one tiny hidden pocket, a hole inside a hole, a sanctuary for a soul to hide from the gods.) 

- he holds the Gate open behind him, for now (again, an indication that he's not in the Void, which would instantly suck the magic from it and from him), but he's curious enough to walk ahead and explore this strange place. 

The roiling energies start to coalesce around Leareth as he walks. There are half-formed shapes that might be living creatures, screams and flashes of light that might be spells. Nothing seems quite real.
Except...there, in the distance, a smudge of green and growing.
He knows that color. The mind-magic that forms the lifeblood of Valdemar.
Leareth stills, eyes narrowing. How has he ended up inside the realm of Velgarth itself?
This plane should be impossible to reach by Gate. The four-leggeds have made certain of that, with protections woven into the very essence of their reality.
Yet here he is.
Interesting.

Here he is! This plane is incredibly confusing, and not especially coherent, and he wants to follow that smudge of green and light in the distance but he doesn't know if he's safe here.

Most mages can't begin the search-spell for a Gate while still holding an entirely separate Gate open behind them, but Leareth is not most mages. He'll try it. If he decides to stay in this place, and go get a closer look, will he be able to leave again safely? 

The world searches back, and finds the Gate - but the protections here don't seem to notice it at all.
This plane is even stranger than it first appeared.
Leareth considers for a long moment. His curiosity is aroused, now, and caution has never stopped him before.
He lets the Gate collapse behind him. The anchor is gone, but he still feels oddly secure on this not-quite-real earth.
The smudge of green is clearer now, and growing. He strides toward it, alert and wary but eager to investigate this impossible new world.

...Huh. 

He'll keep walking forward.

:Is anyone here?: he calls out in Mindspeech. 

There is a flicker of something in the distance, a distant mind that vanishes as soon as he calls out.
But ahead, the green is resolving into a place he knows. Haven - though not as he's ever seen it, more a representation of the idea.
:Who's there?: comes a startled mental voice, and a figure emerges from the half-formed buildings. A Herald, though dressed in antiquated Whites, a style centuries out of date.
The Herald stares at him. :You're not supposed to be here.:

He hasn't been to Haven in person in....gods, nearly eight hundred years. He's scried it from a distance, of course, but still. The vague idealized version feels almost more familiar than the reality he's seen from far away. 

...Does he recognize the Herald's face? 

The Herald looks familiar, like a half-remembered dream, but their mind is closed off. No name comes to Leareth, no flash of recognition.
Just the clear statement, ringing with truth: :You're not supposed to be here.:
"No," Leareth agrees mildly. "I'm not. But here I am - and I would appreciate any explanation you can offer as to how that came to be."
He scans the area again, but there are no further presences nearby that he can sense. "We seem to be quite alone," he observes. "Shall we speak freely?"

"I would like that," Leareth says, quietly. "Tell me - where are we, and why am I here? ...I would assume you brought me here but I am not sure, actually." 

"I did not bring you here," the Herald says flatly. "This place is not meant for your kind. You should not have been able to enter."
They eye each other warily across the distance.
Leareth allows a flicker of impatience to cross his face. "I am aware of that," he says. "The question remains - where are we? What is this place?"
The Herald hesitates, but finally says, "The Pelagirs. The Heartland of Valdemar. The land of the Hawkbrothers, k'Sheyna Vale, k'Valdemar Vale. The place from which all of Valdemar gains its strength and magic."
"Fascinating," Leareth murmurs. His mind is racing with implications, possibilities, dangers. "And we are...not precisely in the Pelagirs themselves, I take it."
"You are not meant to be here at all," the Herald repeats stubbornly. But they glance away, and Leareth knows he's guessed correctly.
"Some representation of it, then. An ideal. A dream."
The Herald says nothing. But their discomfort is clear.
"Well!" Leareth says brightly. "Since I am here, perhaps you might show me around?"

- he didn't say that. It's not something he would say. 

It's like being in a dream, and suddenly being shaken, not awake - it's like the kind of nightmare you can't wake up from on the first try - but to a trapped lucid-dream awareness, that this is wrong and isn't real. 

He switches back to Mindspeech. :What are you doing to me?: 

:Nothing that you do not deserve,: comes the cool mental reply. :You wished to understand the heart of Valdemar. Now you have that chance - though not quite as you imagined, perhaps.:
The churning chaos around them is resolving into something horribly familiar. A memory, dark and twisted.
:We are inside your own mind, Archmage,: the Herald says. :Welcome to your personal hell.:

But what memory? Leareth - is not ready to believe, yet, that this entity, whatever power it has, knows who he is. 

Archmage, it said. 

:I think you may have me confused with someone else: His mindvoice is very mild. :I was never -: well, not entirely true, he's borne the title of Archmage often enough over the centuries, :- in Predain I was not an Archmage. Are you thinking of Urtho?:

The Herald laughs, a cold and terrible sound.
:Do not try to lie to me here,: they say. :I know you, Ma'ar. I know every thought that has ever passed through that twisted mind of yours. And now you will face the consequences of all you have done.:
The chaos around them is coalescing into fire and screams. The memory of a village burning, seen through Leareth's own eyes.
He stumbles back a step, stunned by the vividness, the intensity of the sensations. It's as if he's living it again, the panic and despair of villagers trapped by a ring of fire.
:Just a taste,: the Herald whispers, :of what is to come.:

he doesn't want to be here he wants a different thing to be happening instead of this 

...Why is this happening - he doesn't actually have a good explanation for that - or for the villagers trapped in a ring of fire, that may or may not have happened but he's pretty sure he wasn't personally there to witness it... 

Can he go somewhere else instead? 

The fire rages, heat and smoke and screaming, memories fragmenting and recombining into new horrors.
Leareth stumbles back another step, and then steadies.
This is illusion. He knows that, now, though the sensations threaten to overwhelm him.
He closes his eyes, takes a deep breath of air that is not truly full of smoke, and reaches for his magic.
The protections here are strange, but he is still himself. Still the most powerful mage of this age, or any other.
He rips a hole in the fabric of this not-reality, tearing through screaming memories to find the way back home. The archmage who crafted this trap for him is no match for Leareth at the height of his power, and reality itself rebels against the falsehoods that have been woven here.
Light flares, blinding.
And Leareth stands once more in his Work Room, leaning hard against a table and breathing raggedly.
Safe.
The trap is broken. But what he saw - and felt - lingers.
He knows, now, that he has a dangerous new enemy.