"You can't fly so I don't know how you would help."

"Magic can throw things; if we threw a lot of sand in the air would it make the portal visible?"

"Maybe? It could go through the portal."

"Maybe we could throw a lot of sand, and you could watch from above and see if any disappears."

"That might work!"

"Let's try to use as little magic as possible on this, I don't want to run out of mana in potentially hostile terrain. How high up do you think the portal was, and could you find the area of ground right below it?"

"I can show you about where I think I was when I came through but I know I have something wrong because I haven't found the portal yet."

"Okay. Our mission here is to explore the ruins and look for magic objects, so we can head that way and look for things on the way."

"Okay. Watch," she says, and she flies to her best approximation of where-would-have-generated-the-first-view-of-this-alucine-she-saw.

She's high enough that they probably can't fill that area of air with sand just by loading some onto a spare sail canvas and flinging, but low enough that boosting it with some magic should do the trick. They'll have the setup ready in a few minutes; Cayra might want to get well above her best guess at the portal location so she doesn't get a faceful of sand.

"Okay." She can do that.

Then they will grab corners of the sail and fling the sand up out of it! There's no visible effect of the magic they do at the same time, except that the sand goes way higher than is plausible. (None of it disappears.)

Disappointing. She keeps a close eye on it, waits for them to cover the whole plausible volume from enough angles to be sure.

After a few more rounds they get pessimistic enough about the whole approach not to want to spend any more mana on it. Also they want to explore the ruins for a while before the sun goes down. 

Well that's annoying but she fights down the urge to whine about it. She lands and walks around with them.

They find a device like a tiny guillotine in a building next to where the docks used to be. It turns out to be chargeable with magic and they're very excited! They theorize that it was used for butchering fish.

"How does this magic work?"

"There are two kinds of magic here: personal casting, and artifacts. Personal casting is the one we know about; making artifacts like this is a lost art. How is works is, some people are casters, and they can use mana to do things. Apply forces to objects, make there be more or less of some substance, make things glow or float for a little while, whatever. If you do too much magic you run out of mana and can't do any more for a while; it comes back slowly up to some maximum--it varies by person--and then you don't accumulate any more."

"And learning this doesn't do anything to you?"

"Nope! You get a bit better at using it effectively with practice, that's all."

"I want to learn!"

"I'm afraid you can only learn if you're a caster, but I suppose you might be one. Pay careful attention to what I'm about to do, and tell me if you feel anything."

Once she's definitely paying attention, he picks up a bit of broken cobblestone and makes it glow for a few seconds. There are no sensations involved besides the light.

"I can see it but I don't feel anything."

"Unfortunate but not surprising. Legend says that in ancient times everyone could use magic, but now it's only about one person in twenty."

"Oh. Maybe I could change that about myself but I don't already know how."