I'll just make a guess of the first thing that came to my mind, but so far I don't see whatEdit: This answer was made before the obstacles would behint was given.
What is the world?
The human body.
What is the Center?
The heart.
What am I?
A blood cell.
What are each of the obstacles (both in general and specifically)?
A weir I reach
My path is blocked
'Till doppelganger shows
To help me breach
The door unlocked
Again the river flows
Once enough blood is in the chamber, the heart valve will open and the blood can flow through the arteries.
Another path do we go down
Myself, my brother, spies
A portal in the distance, whence
Decision Maker sighs
The blood needs to go into the smaller capillaries.
Yet when I found myself within
The Center's halls and then
Was counted I, and grouped and moved
I found myself again
Upon a path, that gilded lay
Through alleys far apart
Back to the place where I began
Right back where I did start!
In the end the blood cell reaches the heart once more and will be pumped through the body again.
No idea what the dragon would be in that scenario though and I'm not sure if I'd be specific enough with the other explanations.