The moment i entered the Obsidion Sanctum, i knew i would be able to do something with it. Well, about an hour later, i made a screenshot guide. There is nothing spectacularly interesting in it, but it is an interesting exercise in wall walking, and has some neat scenery.
You can start wherever you please,
but you need to end up on the lava covered hill in the middle-upper part of this.
You can see where i started in the upper left hand corner of the screenshot; it provides perspective. Unfortunately, I used a path which requires blink/autounstuck; there is undoubtably a way around this invisible wall (that you cannot see, imagine that; i assure you there is a wall here) without these two tools, but for the sake of speed i used blink.
Safely on the other side (though it may take a few tries; it took me a few blinks). Climb around the hill to my right, you will see a pool of lava.
There will be a distinct two-tiered hill thing in the distance; that is your next objective
Ah, all apologies, the screenshot here had my name and the name of a friend in it. The screenshot showed me on top of the hill, looking at the two-tiered hill, with a pool of lava betwixt us.
You should be able to swim to the hill no problem, jumping as you go,
Heres the tricky part. When you climb to the top of the hill,
you need to turn around and wall walk over the mountain side, until you are able to get on top of the secondary hill.
Almost there...
All righty, we made it.
Climb up this hill,
Enjoy the scenery.
You can see the rest for yourself, i already put too many images up here.