1-Scorpius Malfoy only sat under the Sorting Hat for about ten minutes before being Sorted into Slytherin because he asked the Sorting Hat what was new, and they talked. He was in Slytherin because Salazar had always been the nicest one to the Hat.
He ended up visiting the hat every month in the beginning because he figured that it would get really bored just sitting in Headmistress McGonagall's office, not being able to move or anything. In the end, it was because they had become friends.
2-Rose Weasley got sent to Headmistress McGonagall's office all the time. On purpose. She had bonded with Fawkes and didn't know a better way to go visit.
It wasn't until she met Scorpius Malfoy, a goody-goody, that she realized that she didn't need to get sent there to go there.
3-Albus Severus Potter liked the portraits the best. In his first year, he got sent there, and he started crying. He remembers hearing a voice that said, "Please tell me you are James Potter. It was bad enough that Potter named one of his sons after me, but if that son was a crybaby, I could never forgive myself."
And then another voice said, "Well, Severus, I seem to recall that you cried the first time you were in here, too." After that, he visited bimonthly. He talked to them all, and then O'd every History of Magic test after that.
4-James Sirius Potter came for the instruments. Those silver thingies that Dumbledore had owned. Eventually, after he had broken one for the fifth time, Dumbledore took pity on him and told him how to use them.
At that moment he was jealous of Al. He wanted to be named after Dumbledore, because, quite frankly, Dumbledore was awesome.
5-Victoire Delacour-Weasley came, not because of anything in there, but because of who was in there. It was the best way to talk to Professor McGonagall about what was going on. She was surprisingly easy to talk to, and really relatable.
Not to mention, she knew what it was like to have a big, famous family. And what it was like to fall in love with the wrong person.
So maybe it was a little weird that her maid of honor was Professor McGonagall, but that was okay. The only one who didn't make fun when the story was related at Christmas was Scorpius Malfoy, Rose's boyfriend (later husband), and Rose herself, because Scorpius's best man was the Sorting Hat, and Rose's maid of honor was Fawkes.
6-Lily Luna Potter felt at home in the Headmistress's office because of the chairs. They were those nice, squashy chintz kind. More than once, she had fallen asleep in those chairs after sneaking into Professor McGonagall's office.
Professor McGonagall was always very nice when this happened.
7-Dominique was always there because of Professor Dumbledore's pensieve. She found it in first year, and when she touched it, she found herself caught in the crossfire of three wizards dueling, while a young witch looked on. She watched one of the wizards, the one with black hair shoot the killing curse at the older auburn-haired one. She watched as he dodged. And then she watched as the young witch repeated the words that the black-haired wizard had said. 'Avada Kedavra'. Even without a wand, it was all the young witch needed to let go of life.
After Hogwarts, Dominique became a famous pensieve expert.
8-Fred Weasley II came because there was the world's best book collection. It was really, really cool. Because really, who else would have a book on the world's worst names (he still thought Al's was a contender), or how to charm pants into cheese or bacon, or how to eat a 23-pound chocolate cake without being sick?
Because of the books, he became fluent in Latin, Norwegian, and Gaelic.
9-Molly Weasley II came for the gargoyle statue that was guarding the door. She had been sent there, but Neville Longbottom forgot to tell her the password, so she stood around talking to the gargoyle. They bonded.
When Molly told her cousins why she came, it's not like they could laugh. Rose came for a bird, after all, and Lily only liked the chairs.
10-It was probably very pathetic, but Roxanne came because of the doorknocker. She had gotten in trouble on her second day, and, looking at the doorknocker, she wondered out loud if she should knock.
"Well, generally, when people come up to a door that is closed, they do knock." the doorknocker had said. "Although I would prefer if you did not bang me against the door with unnecessary force."
Roxanne is sure she was the first to figure out it talked, so she visited it weekly. It was pretty cool to talk to something that nobody thought could talk. She was always one step ahead of the gossip that way, and that doorknocker, DK, was (to use Uncle Ron's favorite term) wicked.
11-Louis came for the desk. It was ancient, and (according to Armando Dippet) was once Rowena Ravenclaw's. It was ancient, yet much more sturdily made than his granddad's desk from Ikea.
Then again, the desk was made with the help of magic, and his granddad's was made with the help of badly-translated instructions in Norwegian.
It was that desk that made him become a famous magical furniture-maker.
12-Teddy Lupin came for the view. It was really nice, and also featured a spectacular view of the Quidditch pitch. It was pretty nice, not to mention that this kept him on top of the other teams.
13-As bad as it sounds, Lucy came because she liked the highly polished oak doors. She liked how when you looked into it, your face is all distorted. She wasn't vain or anything; she just wondered why it was like that.
With the help of Physics for Dummies and Auntie Hermione, she learned why.
After Hogwarts, Lucy Weasley became a famous physicist.
14-Lorcan liked the Sword of Gryffindor. He liked that it was ancient, he liked that it was shiny. And he liked that it belonged to people like Godric Gryffindor and Dumbledore and Harry Potter. It was cool.
And it was deadly. It was the kind of thing that made you want to become a knight and slay rampaging dragons (not that he would tell that to Charlie. Or Hagrid).
15-Lysander liked the horcruxes that were scattered throughout the office. To think that his mum's best friend's husband and his two friends actually destroyed them. When they were seventeen!
It was mind-boggling to think that a bunch of kids had to kill the evil guy with no real help at all. So, after he graduated, he helped out kids by becoming (in their words) 'the best Defense Against the Dark Arts professor of all time!"
16-Hugo came because everyone else did. He had no real attachment, but he felt left-out when everyone disappeared to the Head's office, so he would come.
When Hugo became Headmaster, he realized something-he couldn't care less about the room itself; it was the only place where Scorpius, Rose, Al, James, Lily, Vic, Ted, Lucy, Molly, Lorc, Sander, Dom, Lou, Fred, Roxy, and he were ever in the same place without any sort of argument or tension. It was peaceful, in that room.
In that room, Dom announced she wanted to study pensieves.
In that room, Rose Weasley first kissed Scorpius Malfoy.
In that room, Scorpius Malfoy proposed to Rose Weasley.
In that room, Al decided to become the History of Magic professor.
In that room, Ted decided to become a Quidditch player.
In that room, Lily fell asleep more often than in her dormitory.
In that room, Vic figured out that she loved Teddy.
In that room, Lucy became the first Wizarding physicist.
In that room, Molly made her first sculpture.
In that room, Lorc became a fantasy novelist.
In that room Sander accepted the post of Defense Against the Dark Arts professor.
In that room, Lou made his first table.
In that room, Roxy decided to become a journalist.
In that room, Fred started a publishing company.
In that room, James invented a ring that vibrated when it was near someone who had used one of the Unforgivable Curses.
In that room, Hugo was happy.