He is not immediately evident to any sense other than telepathy.

But telepathy can pinpoint his exact location. ...Which is less helpful when "his exact location" is apparently on the other side of a significant amount of rock and earth. It takes him and Erik several minutes to locate the cave opening.

It's dark in there.

Something looks out at them. Something with huge green-gold eyes and a not particularly human silhouette dimly visible in the darkness.

Fascinating. Beautiful. "Hello!" he calls out cheerfully.

The silhouette shifts. Changing position or changing shape, it's hard to tell. The eyes, at least, remain the same. They blink once.

"Hello," rumbles a deep, amused voice, with a flash of bright white fangs.

"My name is Charles Xavier, and this is my associate, Erik Lehnsherr."

"Why are you here?"

"Erik and I are seeking out other people like ourselves, people with extraordinary abilities."

He laughs. It sounds like the kind of laugh you might ascribe to an ogre or a dragon, deep and loud and wild.

"What for?"

"There is a man," Erik says firmly, "who also has powers, who needs to die."

"Who needs to be stopped," Charles says. It sounds like an old argument. "He's been manipulating international politics for some time--to what ends, precisely, we don't yet know, but not good ones, not for anyone but him."

"Politics," he says contemptuously. "Politics is what I started living in caves to get away from."

"We're not doing politics," he says. "I suppose Charles might be, but as far as the rest of us are concerned, Shaw is the threat."

"What we've observed suggests Shaw is having to keep an active enough hand in everything that the situation will resolve itself reasonably well once he's off the playing field."

"And why should I care?"

"If you like living out in the woods all by yourself with little to no human contact, I suspect you have less reason to care than most. But if you don't--we're building a place where people like us can be, one that will last long after Shaw is gone. You don't have to be alone."

He laughs again.

"I've been alone since before Napoleon's empire. It suits me fine."

"Since--that's amazing," he says earnestly. "What else can you do?"

A movement in the darkness that might be a shrug. "I can fly," he offers as an example.

"Groovy. We've only found one other who can fly, so far."

"Oh?"

"Her name is Angel. She has dragonfly wings that melt into her back so that they appear to be tattoos."

"And she spits fireballs."

"Charming, if limited."

"Most of us are, one way or another. Most have only one ability, though it may manifest in different ways, although Shaw's telepath is proof that entirely disparate powers are possible. In addition to her mental abilities, she has the capacity to transform her body into solid diamond."