"Maybe not," the man says.  "But you're not what your aunt and uncle think you are either.  People're gonna see that in the wizarding world.  Just you wait."

"I guess."

"You mark my words," the man says.  "We oughtta get going."

He raps his knuckles twice on the side of the boat.  The knot tied to the pier..... pops open, somehow... and the rope sort of slurps itself up into a coil behind Harriet, and the boat sets off toward shore.

This is kinda really cool!

"Where're we going?"

"Tonight, we're gonna head to shore and I'll put up a tent for us on the beach.  Not a titchy Muggle tent, a proper three-room one.  Spend the night there.  Then... well, I'll have to talk to you a bit, to know exactly where we're going first.  But that can wait.  Been a big night for you already, after all."

"Wouldn't a three room tent be really big to carry around?"

"Lotta wizard things can hold more than they look like," the man says.

"Cool!"

He chuckles.  "Right useful, too."

She makes a curious noise.

"Well, the more you can fit in a little bag like this," he says, and shakes his knapsack indicatively, "the more you can have with you any time you need it."

"Okay. Like books?"

"Books, supplies, tools.  Tents," he adds wryly.

"Neat. So you can hide magic stuff, too?"

"Lotta magic stuff hides itself, don't it," he says.  "But there's enchantments wizards can put on things to make 'em harder to find."

"Really?"

He nods.  " - Looks like we're here," he says, and indeed the boat's coming up on the shore.

She nods, and waits for it to arrive before clambering out on her own.

Once they're both out of the boat, the man reaches into his knapsack and pulls out a bundle of canvas and tent poles, and tosses it a few feet away from them onto the sand.

"Well, come on then!" he says to it.

It unfolds itself, climbs to its feet, and settles into a tent-shape.  It looks - not any bigger than an ordinary nonmagical tent, actually.

She squints at it, then ducks inside.

It's bigger on the inside!  The outer walls are all sort of hanging canvas curtains but there's two solid inner walls, at a right angle, one across from the entrance and one to the left, that have wooden doors in them; and there's a couch and a couple of comfy chairs as well.

"Woah!"

He grins.  "Why don't you pick out your room."

She goes to explore.

Each door leads to a bedroom.  Left-hand one's a bit smaller.