One red? cube that I found by cheating in some fashion. I saw the 2 red dots in the telescope and thought that it meant LT RT. When that didn't work I consulted a wiki. I'm glad I did because I never would have figured that out on my own. What the hell does this thing do? It's not in my inventory anywhere.
I also discovered the infamous Black Monolith... won't deal with that for now. Lowered the water level and was happy to see so many new doors. Mostly I've been wandering around getting cubes from tetris pieces. My first full page of notes has officially been taken. I discovered the blue rooms with red platforms that flash with the music. That was pretty cool. Though the totems and obelisk there confuse me as to what they actually mean. The tuning forks (I've now discovered 3) are really piquing my curiosity. No idea what to do with them though.
Still no damn clue as to the alphabet or the numbers. Which makes me feel like a large chunk of the game is still hidden to me.
Is this the room that reveals the key to the alphabet... or just another puzzle?
Also: flying is hella useful. I don't even feel guilty about abusing it.