It's a Hogwarts Halloween!
A number of years ago, "The company" started having a Halloween party for the employees and their families. At the time there were 20 employees. Every year it just about doubled in size. There are now several hundred employees. The kids get to trick-or-treat to all of the offices and cube farms that want them. Everything everywhere is decorated. Then they troop to the other wing and get dinner, games, and a magic show in the Activities room. We also turn 2 of the conference rooms in that wing into haunted houses. 1 a little kid scary, the other big kid scary. These are little kids so it's Mr. Toad's wild ride scary - not Alien scary. We don't want anyone in years of therapy! Last year was the haunted pirate ship and the zombie island where she was forever moored... "The company" has also been recently been bought by a conglomorate. They will be shutting this office when the lease is up and moving everyone to a building they own. This means the last "company" Halloween party. - Probably the last Halloween party period.
So we want to go out with a bang. But I need a few more ideas. Luckily, Alz has provided me with a room of requirement, right here, by hosting TFH.
What I've got so far:

Children get a 'portkey' in the lobby. They are sent into the elevator so the Muggles can't see them disapperate.
The elevator doors open in 'London.' (OK, I can dream can't I?)
A right turn down the 'street' takes them to the "Leaky Cauldron" (company Lobby, which oddly enough actually looks like a bar...)
through the brick wall to Diagon Alley (Development)
They trick-or-treat through the various 'shops'.
At Gringott's (the CFO's office) they take a wrong turn down Knockturn Alley (Support) They trick or treat here too, being careful to avoid "Borgin and Burkes" (VP of new product development - the darkest magic!)
This will eventually spit them out in King's cross station (building hallway with the public bathrooms) Through the barrier at the end to platform 9 3/4 "hogwarts Express" is going to be on the glass of some empty office space.
By the time they walk to the other end of the train they are at Hogwarts. (Sales)
The Activities room is being turned into the great hall enchanted star-lit ceiling and floating candles. (A lot of plastic and black thread) and Gryffindor colors.
1 conference room is likely going to become the potions classroom. (We did Mad Scientist a few years back - so I can recycle a lot of stuff there!)
The other - I'm stuck and need ideas.
I also need ideas for games.
I thought we *might* (said with a wince) be able to do quidditch 'pre-qualifying' tryouts with 'nerf' balls throw it through a hoop for chasers, hit it with a plastic bat for beaters, catch it for seekers and keepers. But there are SOOO many kids now, I'm afraid - very afraid....
1 conference room is about 20x15 you enter one corner exit the opposite side.
the other conference room is about 25x12 with only 1 door.
What we've done the last couple of years is built a small atrium then split the room length-wise floor to ceiling so the kids walk in and down one side and cross through and back up and out the other - a big U.
And so I need ideas. I need IDEAS. I NEED ideas!
Also - How do I decorate 'London' ?????!