Similar to the concept of Endless Tower of Boss battles BUT WITH PUZZLES! Basically, just say how you would solve the puzzles, then at the end of your post, put what the next floor would be.

Floor 1: A normal door with the word "Welcome" written on it.

edited 9th Oct '11 1:35:39 AM by Kexruct

I'd open the door and go in; clearly I am welcome.

A door with no handle, an enormous, locked chest against the wall, and a single rusty key.

Though my initial instinct is to merely unlock the chest and retrieve the handle, that proves fruitless. The chest is empty save for a small hammer. Following a hunch, I take the hammer, and (using the key as a chisel) carve the word "Welcome" onto the door. The handle appears.

A locked door made of strong metal, and a piano in the corner with "Largo" painted across the keys.

I press a random F key, for Florida.

Floor 4: There is no apparent door. However, on closer inspection, you find a hole in the ceiling that apparently leads to the next floor. In the corner of the room there are several boxes with climbing equipment, but all of them are sealed.

Stack the boxes to climb up.

The next room is full of lions, tigers, bears, oh my! You have only a pair of nail-clippers and a match (not a strike-anywhere one, either). The door is a normal door but the lions, tigers, bears, oh my! are in the way. What do?

Walk around the lions, tigers and bears, oh my!, they're actually completely harmless unless aggressed.

6F: The room is empty except for the door, which is on the ceiling.

Realize that gravity is not the same and moon walk to the door.

Floor 7: There are three objects and three slots. The objects are a cylinder, a cube, and a pyramid. The slots are a circle, a square, and another square. Wait a moment, something's not right.

Something is right; the pyramid is a square pyramid. I fit the three shapes in the holes and the door swings open by itself. Somehow.

8F: The room is empty except for a board standing up in the middle of the room.

The board is actually the door, which has been misplaced. I move it back to the wall and I can walk through the door to get to the next floor.

Floor 9: There are three potions and a revolver on a table in front of the door to the next floor.

Just walk past them and go through the door. They don't mean anything.

10F: Three potions and a revolver. No door.

First potion turns my eyes into Lens of Truth, seeing a hole, but breakable and small. I used the revolver and use the second potion to turn myself into a tiny person, falling into the next floor, causing a elevator for me to the next floor. Third potion turns me back to normal.

Next floor: Bomb flowers everywhere, but gap in middle. The only thing you use is a bomb.

edited 9th Oct '11 4:18:05 PM by Aniventerie

I eat it. In front of me appear the words "because lololololol" and the entire wall retracts.

13F: A bottomless pit.

Fall down and land on the fourteenth floor. Somehow you fall up a floor instead down.

F14 Three boys are present. Boy 1 says the door won't open unless Boy 2 says so. Boy 2 says Boy 1 is lying. Boy 3 says Boy 1 is telling the truth? What do meng?

edited 9th Oct '11 4:32:43 PM by Rivux

First, i divide the boys in two groups:
Boy 1 and 3: Boy 2 is lying
Boy 2: Boy 1 (And per extension 3) is lying.

Taken that only one boy is lying, that means that boy 2 must be lying, in which case i... convinve him to open the door for me.

Floor 15: You start out on a platform with a narrow path leading to the next door. Said path has no ledges to prevent you from falling. On the sides of the room, there are isolated rooms with ridiculously cute kitties.

edited 10th Oct '11 1:35:19 AM by neobullseye

I just crawl. That was easy.

Floor Sixteen: The floor is a white room with nothing inside. Literally, nothing. No objects, no door, even the entrance vanishes behind you. All there is is six white walls and yourself.

The walls are illusions. I knock on the walls, relying on sound instead of sight. I find the door, open it and go through.

Floor 17: This puzzle is a test of your recognitino of deities in fiction. The door will not appear until you achieve at least a 50% on the test and there is no alternative. Better hit the trope pages, since there is a laptop and mouse provided.

I use the power of the mighty GOOGLE to answer the questions. A bit time consuming, but easy.

Floor 18: There is a television screen in the center of the room. The door is just beyond it. A red button is below the screen. Every time it is pressed, the TV goes up one channel.

I press the button until it's on Channel 18; the door clicks open. Not too shabby.

Floor 19: The door is to your left when you enter. Or so it seems; you're in a hall of mirrors. Just kidding, some mirrors are mirrors, and others are portals that will you lead out into the previous floor. What do you do?

I go through a regular mirror reflecting a portal-mirror. The reflection of -1 (that is, going down a floor) is 1 (going up a floor).

Floor 20: In the center of the room is a lamp. On, the door is locked. Off, the door is unlocked but leads back to floor 20.

edited 10th Oct '11 2:54:32 PM by Aniventerie

I take the lamp with me, turn it on, walk through the door, and then turn it off, letting the door close behind me, and letting it lead to the next floor.

Floor 21: Ye find yourself in yon dungeon. Ye see a SCROLL. Behind ye SCROLL is a FLASK. Obvious exits are NORTH, SOUTH, and DENNIS.

Take fla- never mind.

I go the DENNIS way, because it sounds weird. It leads to a scroll-shaped enclave in the wall. I put the scroll in and the wall opens.

21F: A bunch of video game discs are scattered on the floor and the door will not open unless you put them in the correct order.

I organize them according to the Hopey Scale.

22F: The floor is filled with movable portals, all of which lead to random previous floors. Not one leads upward.

(Guys, we're a number behind. This is floor 23.) I walk past the portals and walk through the door.

Floor 24: There's a disassembled computer on a desk with a post-it that reads "Power on for padlock combination". There is no lock on the door.

edited 10th Oct '11 4:00:26 PM by VmKid

(No we're not, Werty accidentally put 21 instead of 22) Then open the door and proceed, if there's no lock, there's nothing stopping you.

Floor 25: Oh dear, it seems there's nothing in here that could possibly help us get to the next floor! What sort of meta properties could possibly help here?