Is there a safe way to do that?

There is a distance where you feel it without vanishing it. Children play games of chicken with that. And if Trevor carries them to the sky and goes far enough that they vanish, they are just going to reappear in a sky somewhere. It's safe.

Then they are fascinated! 

In that case they get to experience the wonder of being near the edge.

Dimensions generally look like they just go on forever. One wouldn't guess that the horizon is "false". Not until you get close enough that things start getting gray, like in a weird sudden mist and if you go further than that there is a sense that can be accurately described as "unreality", of being near something that is not. If anyone wants to actually vanish Trevor is happy to carry them (extra benefit of flying) and the sense of unreality greats stronger until it feels like there is no gravity for a moment... and then they reappear minutes later, but with a subjective experience shorter than that. It's a very unique experience. They can totally believe that the majority of small children and all animals just avoid going near an edge entirely.

They believe it!

He is glad. They are going to need to put that stuff on brochures. Eventually, they're going to teach this sort of thing in middle-school.

Oh, and since everyone (including Isel) is around. Trevor kind wants to share this fact that he didn't share earlier with her. Now that people here know what it feels like to dreamshape, to take that vast sea of energy and give it form and how much it can made. Well, Trevor would like to announce that Fenris' form of immortality takes 200 hours of sleep to produce a single unit (a floating rock) and since Fenris is efficient it's more like 250 hours of magic energy all concentrated on a thing the size of a house. He is saying this mostly because he is curious about the look on their faces, not a way to brag how immortal the Dalkaila are.

They now have enough understanding of magic to be highly impressed at what it'd mean to have it concentrated like that. 

    "Does doing that mean you're not expanding your dimension," says Kantil. 

    "Can other people replicate that?" asks Kefin.

    "In general can you get stronger effects by concentrating them?" asks Afen, frowning. "And what contributes to efficiency -"

"That is Fenris, he is in fact not expanding his dimension while focusing the energy like that. Except when he actually manifest the floating rock."

"Presumably someone can. It happened once after alll. Maybe not the exact same way. It also does skymagery to people that don't have it yet. But that only adds to a couple of hours to the total."

"Stronger effects require more magic in general. I think it might be an affinity or personality thing. Fenris is very, very, very, very, very," he makes a show of taking a deep breath, "very, very, very intense about improving things and what it means for something to be flawless. So his method of immortality is suitably intense."

"How long did it take to invent in the first place?"

"It just started with immortality, a weaker version that got stronger overtime. But Fenris improved features like a memory boost every time you die, allowing people to shape their new bodies, you can keep or remove scars and tattoos as you please or get back in a fit body. He was working on transition too. It also lets you pick and choose long-lasting magical effects in the same way as the body modifications. And he also added things like the superluminal connection and correcting the effects of mental tampering. This actually cut off the overall time it takes to create a new fountain."

"But how long did it take to get the original?"

"It produced two fountains at once when it started, They're just not as strong but the dimension let him direct energy to them. And once those are metaphorically fully mature it let him create a third, which had the time typical constraint."

"The thing I'm interested in is how long it'd take one of us to have something that did immortality."

"Ah, of couse. Something that does what Fenris' does and wasn't obnoxious about it would take twenty hours per immortal. Might get less or more if you had something communal."

"And would someone have that in twenty hours of trying, or would it take longer to learn how to do that with magic -"

"Ah, sorry, twenty hours of making the unit once you have it. I hooooonestly can't guess how long it would take once learning."

"How long has Fenris been at it?"

"Less than a year. Unsure how long he is going to need to work at it. His dreamshaping is uncooperative on purpose."

"Less than an Earth year?"

"Oh, yeah, less than a season here."

"In that case several of us should probably focus on getting useful magical effects in our dimension."

"Government's going to consider that one vaguely unfriendly."

"Hmmph."

"There might be modifications that'd make it acceptable. Can't be killed except in one way they have access to."

"Heh, I for one would welcome the good company in the next long decades. Aaaaand interworld travel would be good if anyone manages it. Fenris would fork yesterday if it meant Felix wasn't alone here."