riddle - A Thing Of Beauty Is A Joy Forever!

I...I've just seen something. Something wonderful. Something beautiful. I don't know what it is...I don't have the least idea, to be honest. But, its innate beauty is unmistakable.

$\qquad\qquad\quad$

But I don't remember what it was like...I have such a bad memory! And it's troubling me a lot - so much, that I've decided to go there again. This time you will come with me. You will, right?

And oh, you may take this conversion table. I don't know what it's good for...but, you'll need it.

    A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z
1   t   2   r   v   P   6   a   Q   Z   5   M   s   g   w   i   j   d   x   m   p   1   f   0   G   e   W
2   k   l   d   w   R   U   C   y   t   Q   j   8   0   9   h   z   c   e   p   u   2   X   P   m   F   w
3   2   e   T   Y   h   x   9   Y   U   C   m   d   E   q   t   W   s   u   G   T   I   K   b   x   7   e
4   w   V   Q   9   o   p   d   g   H   M   S   Y   6   b   r   y   5   4   t   q   E   c   4   d   N   M
5   a   v   i   g   r   a   i   l   Q   X   Z   w   d   t   7   d   5   3   x   Y   0   K   J   F   b   s
6   6   w   F   l   c   q   l   K   I   g   T   Y   v   s   Q   Z   a   w   B   j   u   c   r   w   V   Q

So, what are you waiting for? Click on me above, and begin your journey!

---

It seems like people are stuck with the final part of the puzzle, so here are some hints. Don't look at them if you want to solve the first few parts on your own.

Room specific hints:

1. 
   

   
   

   "Hey,buddy...": Think steganography. Think rand al'thor.

   
   

   
   



2. 
   

   
   

   "I live in...": It might be easier to solve the other parts first and then reverse-engineer this one.

   
   

   
   


3. 
   

   
   

   "This will...": Follow the instructions. MOehm has a useful idea in chat, but he's missing something.

   
   

   
   



4. 
   

   
   

   "Do this..." and "All you've...": Quite straightforward; think literally.

   
   

   
   

Overall:

Do you remember anything famously beautiful, that resembles the relative positions of the rooms?

Answer

(OP Edit: This answer solves the final (and crucial) part of the puzzle. For a complete answer, please see BeastyGerbil's answer, which includes the works of BeastlyGerbil, olesaw, MOehm and Xenocacia.)

I feel bad posting this as an answer when other people have done so much of the work, and I'm missing some of the details, but I believe the answer to the final riddle is

Euler's famous mathematical formula $e^{i\pi}+1=0$

which is widely considered

one of the most beautiful things in all pure mathematics. (Clues in that direction: all the talk of beauty and depth, with the suggestion of timelessness in the title's Keats quotation; the graph-paper aesthetic in the pictures, suggestive of mathematics generally and 2-dimensional geometry -- hence complex numbers -- more specifically. Perhaps "my eyes" in the last panel is meant to be a bit of a hint towards $i$.)

Its shape corresponds loosely to that of the building we have been through, and each room's riddly sign clues one part of it.

First room: "Hey, Buddy! Do you really know who I am? No? Alright, I will tell you all about myself. Okay, listen. I am now describing myself, bit by bit. Seriously. I hope you are following me so far? That's great ..."

This describes $e$. The sentences contain successively 2, 7, 1, 8, 2, 8, 1, 8, 2 words, and the decimal expansion of $e$ begins 2.71828182. (Thanks to oleslaw for spotting this; I looked at letters per word but not words per sentence, a longstanding blindspot of mine now I come to think about it.)

Second room: "I live in your imaginations."

$i$ is the canonical imaginary number.

Third room: "This will make your head spin! d"

Clearly something to do with $\pi$, but I confess I'm not sure exactly what beyond the obvious remark that spinning and $\pi$ both have something to do with circular motion. Perhaps the "d" signifies diameter? Or maybe there's something anagrammatical going on ("pi" is contained in "spin", but that may be pure coincidence). M Oehm suggests that perhaps the "!d" at the end is meant to be viewed upside down (having spun one's head) to make "pi". I really hope not, but it's certainly possible.

Fourth room: "Do this if you like this."

"+1", fairly commonly used to mean upvoting or other sorts of approval and Google+'s equivalent of the Facebook "like".

Fifth room: "All that you've seen so far are worth nothing."

"=0". That is, the previous stuff turns out to equal zero.

(I am in no way satisfied with what I've said about room 3 and am still thinking about it.)