The hole? It's easy for me!
See the point where the two sides of the room meet at the side you face when you enter the room?
|-________-|
|___-__-___|
|____|_____|
|____|_____|
|____|_____|
_____o
____\|/
The yellow "line"? That's the one. The blue is Sonic. That's a third-person view.
Right on that line, on the floor, is the center of the hole. That's the center of the room. The hole is in the center of the room. It's aligned with the center "tile" of the ceiling flat.
______/\
_____/_|_\
____/__o__\
___/__\|/___\
__/____|_____\
_/_____|______\
/_____|_|______\
\______________/
_\____________/
__\__________/
___\________/
____\______/
Bird's-Eye View. The blue is Sonic, the orange is the trail you should follow, yellow is the hole, brown is the center, and light-purple is the outside. Get my drift? ;P
I apologize. I'm just in an artistic mood this morning :/