They clamber up a passageway in the rock after Hagrid's lamp, coming out at last onto smooth, damp grass right in the shadow of the castle.

They walk up a flight of stone steps and crowd around the huge, oak front door.

"Everyone here?" And before waiting for an answer Hagrid raises a gigantic fist and knocks three times on the castle door.

The door swings open at once. A tall, grey-haired witch in emerald-green robes stands there. She has a very stern, almost stereotypical witch face.

"The firs' years, Professor McGonagall."

"Thank you, Hagrid. I will take them from here."

She pulls the door wide. The entrance hall is big enough you could fit the whole of the Dursleys' house in it. The stone walls are lit with flaming torches like the ones at Gringotts, the ceiling too high to make out, and a magnificent marble staircase facing them leads to the upper floors.

That's a big magic castle.

Indeed it is.

They follow Professor McGonagall across the flagged stone floor. They can hear the drone of hundreds of voices from a doorway to the right—the rest of the school must already be here—but Professor McGonagall shows the first years into a small, empty chamber off the hall. They crowd in, standing rather closer together than they would usually have done, peering about nervously.

"Welcome to Hogwarts," she says. "The start-of-term banquet will begin shortly, but before you take your seats in the Great Hall, you will be sorted into your Houses. The Sorting is a very important ceremony because, while you are here, your House will be something like your family within Hogwarts. You will have classes with the rest of your House, sleep in your House dormitory, and spend free time in your House common room.

"The four Houses are called Gryffindor, Hufflepuff, Ravenclaw, and Slytherin. Each House has its own noble history and each has produced outstanding witches and wizards. While you are at Hogwarts, your triumphs will earn your House points, while any rulebreaking will lose House points. At the end of the year, the House with the most points is awarded the House cup, a great honor. I hope each of you will be a credit to whichever House becomes yours.

"The Sorting Ceremony will take place in a few minutes in front of the rest of the school. I suggest you all smarten yourselves up as much as you can while you are waiting."

Her eyes linger for a moment on Neville's cloak, which is fastened under his left ear, and on Ron's smudged nose.

"I shall return when we are ready for you. Please wait quietly," she finishes, and leaves the chamber.

...perhaps Neville would like some help with his cloak?

Neville would like some help with his cloak, yes.

There, now it sits right. And how about Ron and his nose, does he want any help with that?

Um maybe.

Nothing two seconds with a handkerchief won't fix. There. He is now smudgeless.

The other students seem to be panicking about how they're going to get sorted into houses. There's talk about it being a test of some sort.

Nothing he can do about that, whereas crooked cloaks and smudged noses are a thing he knows how to handle.

Muninn preens Victor's hair and croak-whispers, "No trouble, boss."

Suddenly several people behind them scream, and when they turn to look, they see that about twenty ghosts have just streamed through the back wall. Pearly-white and slightly transparent, they glide across the room talking to one another and hardly glancing at the first years. They seem to be arguing. What looks like a fat little monk is saying: "Forgive and forget, I say, we ought to give him a second chance—"

"My dear Friar," answers a ghost wearing a ruff and tights, "haven't we given Peeves all the chances he deserves? He gives us all a bad name and you know, he's not really even a ghost—I say, what are you all doing here?" he asks, finally noticing the first-years.

"What's it to you?" croaks the raven on Victor's shoulder.

"New students!" says the Fat Friar, smiling around at them and seemingly ignoring the raven. "About to be Sorted, I suppose?" And then he peers at the raven. "And I didn't know they were allowing ravens again! I wonder why they ever stopped."

"I'm the prettiest," he says smugly.

"Of course you are," he says, smiling kindly, then looks at Victor. "Hope to see you in Hufflepuff! My old House, you know."

"Move along now," says a sharp voice coming from the door—McGonagall, returned. "The Sorting Ceremony's about to start." One by one, the ghosts float away through the opposite wall. "Now, form a line," she tells the first years, "and follow me."

Easy enough.

They walk out of the chamber, back across the hall, and through a pair of double doors into the Great Hall.

It's lit by thousands and thousands of candles that are floating in midair over four long tables, where the rest of the students are sitting. These tables are laid with glittering golden plates and goblets. At the top of the hall is another long table where the teachers are sitting. Professor McGonagall leads the first years up here, so that they come to a halt in a line facing the other students, with the teachers behind them. The hundreds of faces staring at them look like pale lanterns in the flickering candlelight. Dotted here and there among the students, the ghosts shine misty silver. Instead of a ceiling, there is a velvety black emptiness dotted with stars, the Great Hall looking like it simply opens on to the heavens.

Professor McGonagall silently places a four-legged stool in front of the first years. On top of the stool she puts a pointed wizard's hat. This hat is patched and frayed and extremely dirty. Aunt Petunia wouldn't have let it in the house. 

For a few seconds, there's complete silence. Then the hat twitches. A rip near the brim opens wide like a mouth—and the hat begins to sing:

Oh, you may not think I'm pretty,
But don't judge on what you see,
I'll eat myself if you can find
A smarter hat than me.

You can keep your bowlers black,
Your top hats sleek and tall,
For I'm the Hogwarts Sorting Hat
And I can cap them all.

There's nothing hidden in your head
The Sorting Hat can't see,
So try me on and I will tell you
Where you ought to be. 

You might belong in Gryffindor,
Where dwell the brave at heart,
Their daring, nerve, and chivalry
Set Gryffindors apart;

You might belong in Hufflepuff,
Where they are just and loyal,
Those patient Hufflepuffs are true
And unafraid of toil;

Or yet in wise old Ravenclaw,
If you've a ready mind,
Where those of wit and learning,
Will always find their kind;

Or perhaps in Slytherin
You'll make your real friends,
Those cunning folk use any means
To achieve their ends.

So put me on! Don't be afraid!
And don't get in a flap!
You're in safe hands (though I have none)
For I’m a Thinking Cap!

The whole hall bursts into applause as the hat finishes its song. It bows to each of the four tables and then becomes quite still again.

Well that's mildly unsettling.