Underground Chambers

The Underground Chambers were a series of rooms below Hogwarts School of Witchcraft and Wizardry, serving as the defences protecting the Philosopher's Stone from 1 August, 1991 until 4 June, 1992. There were a total of seven chambers, each of which containing an obstacle or task that guarded the Stone and delayed any intruder.

Background
In 1991, the Philosopher's Stone became the target of Lord Voldemort due to its potent ability to return him to full power. Suspecting danger, Albus Dumbledore set out Rubeus Hagrid to retrieve the Stone from Vault 713 at Gringotts Wizarding Bank the same day he took Harry Potter to Diagon Alley. That same day, Quirinus Quirrell, who was being used as a parasite of Lord Voldemort, broke into the bank, but failed to obtain the Stone.

Thereafter, Hagrid brought the Stone to Hogwarts as requested, and Professors Pomona Sprout, Filius Flitwick, Minerva McGonagall, Quirinus Quirrell and Severus Snape, as well as Hagrid and Dumbledore themselves, created each their own separate chamber.

First


The only known way to access the Stone was through a trapdoor in the Third Floor Corridor, which was guarded by the three-headed dog Fluffy. Fluffy had been purchased by a Greek man in the Hog's Head Inn by Rubeus Hagrid, and was later put into the third floor. To get past this obstacle, one had only to play some music, which would then put Fluffy to sleep.

Second


After going through the trapdoor, a long and dark drop through the air led into a chamber full of Devil's Snare, planted by the Herbology teacher Pomona Sprout. The plant was designed to entangle and suffocate any intruders, especially quickly the more the intruder tries to escape. Bluebell Flames, however, could be used to repulse them.

Third


"They're not birds! They're keys! Winged keys - look carefully. So that must mean ... Yes - look! Broomsticks! We've got to catch the key to the door!"

- Harry

A downwards sloping passage with stone walls, through which trickling water could be heard, led to a brilliantly lit chamber with a very high ceiling, full of glittering winged keys, charmed by Filius Flitwick. On the opposite end of the chamber from the stone passage was a large, old-fashioned wooden door with a silver lock that would not open, even with the Alohomora Charm, without the necessary key. One had to mount a broom and attempt to pursue the correct key; all of the keys fluttered away quickly, darting around, making it very difficult to catch the correct one.

Fourth


"I think we're going to have to be chessmen."

- Ron

The next chamber was so dark that it was impossible to see anything. It contained a Human Chess Game, which had been enchanted by Minerva McGonagall. To get across the chamber, one had to checkmate the King according to the rules of Wizard's Chess.

Fifth


After that came a chamber containing a mountain troll that needed to be knocked out in order to pass; it had a foul odour in it, and it was said that there was great relief in passing through it.

Sixth


"Brilliant. This isn't magic - it's logic - a puzzle. A lot of the greatest wizards haven't got an ounce of logic, they'd be stuck in here for ever."

- Hermione

The second-to-last obstacle guarding the Stone was a logical riddle set by Severus Snape. Upon entering the chamber, the entrance was blocked by purple flames, whilst the exit was covered by black flames. A table holding seven bottles of differing shapes and sizes sat in the centre of the room.

Each bottle contained a liquid, but the bottles were not labelled with their contents. Three were poison, two contained nettle wine, one contained a potion to safely traverse the black flame, and the last contained a potion that allowed passage back through the purple flames. The riddle, when properly worked out, revealed the contents of each bottle, and therefore which one was safe to drink to allow onward progress:

"Danger lies before you, while safety lies behind, Two of us will help you, whichever you would find,  One among us seven will let you move ahead,  Another will transport the drinker back instead,  Two among our number hold only nettle wine,  Three of us are killers, waiting hidden in line.  Choose, unless you wish to stay here for evermore,  To help you in your choice, we give you these clues four:  First, however slyly the poison tries to hide  You will always find some on nettle wine's left side;  Second, different are those who stand at either end,  But if you would move onwards neither is your friend;  Third, as you see clearly, all are different size,  Neither dwarf nor giant holds death in their insides;  Fourth, the second left and the second on the right  Are twins once you taste them, though different at first sight." [src]

Based on Hermione's deductions, from left to right, the potions lineup is:
 * 1) Poison
 * 2) Nettle wine
 * 3) Potion to move the drinker forward through black flames
 * 4) Poison
 * 5) Weedosoros
 * 6) Nettle wine
 * 7) Potion to move the drinker backwards through purple flames

Seventh


The final obstacle was the Mirror of Erised, designed and set by Albus Dumbledore. The only way to obtain the stone was for an individual to look into the mirror and see themselves possessing the stone but not using it.

Behind the scenes

 * The prevalence of the number seven is not coincidental; seven obstacles were in place to get to the Philosopher's Stone and seven different potions were available in Snape's logic riddle. Seven, as deduced by Arithmancer Bridget Wenlock, has magical properties to it. It is believed that the number seven is the most magical number. It is also, of course, the total number of books in the series, with Rowling firmly sticking to that number.
 * The fifth and sixth obstacles were cut from the film. The potions riddle, however, was later shown in the second disc.
 * There were a lot of differences in the Chambers between the books, films and video games, shown in the following table:

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Philosopher's Stone (video game)
 * LEGO Harry Potter: Building the Magical World
 * LEGO Harry Potter: Characters of the Magical World
 * LEGO Harry Potter: Years 1-4
 * Pottermore
 * Harry Potter LEGO Sets