When you finish your Defence Against the Dark Arts Class and exit the room, you will be confronted by Hermione Granger, a whiz at magic. Follow her to the Potions class in the Dungeons. There is a save point at the stairs to Floor 2, so use it. Now descend.
Peeves the poltergeist again. Just ignore him and go down 2 more flights of stairs.
Here, you'll meet Hermione at the bottom of the stairs. Follow her to the left of this floor and enter the room into the...
Upon entrance, find your way to left, where you'll see a door with a shield on the wall beside it. Enter the door to Potions class. If you want, you could save at the save point just north of the entrance into the Dungeons, or grab the Pumpkin Pasty in the northern area of the Dungeons.
You walk automatically towards a gathering of students, where a bubbling cauldron sits. Professor Snape is the teacher and seems to bear a grudge towards you. He welcomes you with open stairs leading deep into the dungeons and orders you to find 6 glass vials.
Find the Glass Vials!
You have been ordered by Snape to find 6 glass vials for Potions class. You cannot leave until you have found all of them.
1. When you enter this new area, break the three pots to the left of you. One of them contains a glass vial.
2. Enter the doorway and turn right. Flip the switch using Flipendo and cross the bridge. Then press the pressure plate (a grey button in the ground) to open one of the three closed portcullises. Enter the open doorway, go through the narrow passage, cross the bridge and press the pressure plate to let out three golden gnomes. Knock all of them out (if at any time you need refuge, duck into the cells you have opened.), cross the bridge to the right, and take the second glass vial.
3. Now press the pressure plate and go back to where there were three closed portcullises (not the cells where the gnomes were held, but the beginning of finding the second glass vial). Enter the second opened portcullis and you find yourself in a room with three barrels and three pressure plates. You can't hold down all three buttons, so use Flipendo to push the barrels over the buttons. Search the bookcase on the right for a bag of Jellybeans (restores a few Energy Bolts) and break the two clay pots for a glass vial.
4. By holding down all three pressure plates, you throw open another portcullis near the entrance of the room with three barrels and three pressure plates. Enter that door to find an easy glass vial and press the pressure plate inside.
5. Go back to the room with three portcullises (again, not the ones with the cells containing the gnomes) and you'll find the last one is open. Go through, push the Flipendo blocks with Flipendo and cross them. Break the 4 clay pots for a glass vial and press the Flipendo switch on the wall.
6. Enter the newly opened door to the south and go along the narrow path. Use Flipendo to push the the barrel and knock out the 3 golden gnomes on the way. Collect the last glass vial in the room.
Snape will then order you to return to class, so pick your way back carefully to the entrance where you started to find the glass vials.
"You collected all six vials! Maybe Snape will go a little easier on you now."
Returning to your Potions class, Snape will give you an assignment: find all the ingredients to make the Wiggenweld Potion - Dittany, Moly, Flobberworm Mucus and Wiggentree Bark. You'll have to find each one in turn. Now exit the Dungeons.