He was standing in a room the size of a large cathedral, whose high windows were sending shafts of light down upon what looked like a city with towering walls, built of what Harry knew must be objects hidden by generations of Hogwarts inhabitants. There were alleyways and roads bordered by tetering piles of broken and damaged furniture, stowed away, perhaps, to hide the evidence of mishandled magic, or else hidden by castleproud house-elves.
There were thousands and thousands of books, no doubt banned or graffitied or stolen. There were winged catapults and Fanged Frisbees, some still with enough life in them to hover halfheartedly over the mountains of other forbidden items; there were chipped bottles of congealed potions, hats, jewels, cloaks; there were what looked like dragon eggshells, corked bottles whose contents still shimmered evilly, several rusting swords, and a heavy, bloodstained axe.
Harry hurried forward into one of the many alleyways between all this hidden treasure. He turned right past an enormous stuffed troll...
...ran on a short way, took a left at the broken Vanishing Cabinet in which Montague had got lost the previous year...
...finally pausing beside a large cupboard that seemed to have had acid thrown at its blistered surface. He opened one of the cupboard's creaking doors: It had already been used as a hiding place for something in a cage that had long since died; its skeleton had five legs.
He stuffed the Half-Blood Princes book behind the cage and slammed the door. He paused for a moment, his heart thumping horribly, gazing around at all the clutter. . . . Would he be able to find this spot again amidst all this junk? Seizing the chipped bust of an ugly old warlock from on top of a nearby crate...
...he stood it on the cupboard where the book was now hidden, perched a dusty old wig and a tarnished tiara on the statues head to make it more distinctive, then sprinted back through the alleyways of hidden junk as fast as he could go, back to the door, back out onto the corridor, where he slammed the door behind him, and it turned at once back into stone.
Some additional pics of the mess:
I really enjoyed building all this junk, although the book-piles kept collapsing to my great annoyance. This build is not really based on the film, its how I imagine the place. Things are not placed exactly as in the book, although I tried to be reasonably accurate.
Sorry for being late. Hope you like it!!!!