Ron is waiting for you, and tells you of a secret bookcase which leads directly up to Floor 7. He leads you to the bookcase, which you must search. It slides away to reveal a stairway, which you proceed into and climb a few steps to...
Hermione is now waiting for you as you emerge, and tells you the password to the Common Room, "Pig Snout". She and you go into the Common Room, and you ask her to teach you the Alohomora charm for opening certain doors. Follow her wand movements. If you get all three wand movement sets correct, she gives you a Pumpkin Pasty.
"You learned Alohomora! This should really open doors for you!"
After learning it, she makes you promise not to use it to sneak around Hogwarts (the exact opposite of which you will be doing) and leaves. Ron tells you to go for the Wizard's Duel now, and you say that you are going alone. If you want to save, go into the room in the northern part of the Common Room. Now, exit the Common Room.
Oop! The whole place is dark. It's night, and most students have turned in by now! Although the whole place is dark, you can still see the silhouettes of prefects guarding the corridors. Don't let them get too near.
1. From your Common Room, go down out of the door and to the left past the bookshelves.
2. Now take the first path upwards and go downwards the other side. Open the locked door with Alohomora and go through the doorway.
3. Walk upwards, weaving past the two prefects walking beside the pillars and take a left at the top.
4. Now go downwards at the other side and dodge the prefects walking between the walls.
5. Maneuver around another two prefects patrolling a corridor with purple drapes and to the right, where you'll find a locked door at the end of a corridor.
6. Open the door with Alohomora, go through, to the right and downwards down the stairs.
1. Go to the left and upwards past the flight of steps.
2. Avoid the prefect in the wide corridor by ducking into the alcoves as he walks past. Then follow the corridors and go upwards.
3. There will be another prefect patrolling around here. Avoid her and go to the right into a narrow passage.
4. Avoid the prefect and go downwards into the first downward-leading corridor you see. It's a long walk downward.
5. When you get to the bottom of the corridor, follow it and elude the prefect by ducking into an alcove. Then go downwards and to the left, and there's the stairs!
1. Go to the left and avoid the prefect by ducking into an alcove. Then go upwards.
2. Keep going upwards through doorways until you reach an area with pillars. There are prefects walking around, so weave past them and go to the right, where you'll find a Flipendo in a small alcove.
3. Flip the switch and go back to the right and downwards into a corridor. Keep right and you'll reach a chasm with the bridge flipped the correct way round. Cross the bridge to the other side.
4. Now there are two ways to go right - take the top path and avoid the prefect when she passes by by going into an alcove.
5. Walk right and downwards past a bookcase and cast Alohomora on the locked door at the end. Go through and downwards, and you'll have a clear way to the staircase.
1. Turn right and cast Alohomora on the big mirror to open up a secret door.
2. Go through the doorway and along the passageway, avoiding the prefect as she passes by ducking into an alcove. Go left and upwards.
3. Now make a right turn and keep walking until you reach a gargoyle and a pressure plate. Cast Flipendo on the gargoyle to activate it, then go upwards and to the right and downwards to find a locked door. When the gargoyle moves over the pressure plate, the door will open and you can run through.
4. Go right and take the upper path to the right, where you'll find another gargoyle. Activate the gargoyle and run past it and downwards.
5. Avoid the prefects as they stroll by in the passageway and go downwards and left.
6. When you emerge from the passageway, keep going downwards until you find a locked door (or open if the second gargoyle you activated is over the pressure plate).
7. Now press on left until you find the stairs to Floor 3. From here, it's easy enough to find the Trophy Room. It's on the left of Floor 3. I don't think a step-by-step is needed here, honestly.