This is known as the theory of Intersecting Points.
In mid-update: 5-17-08
I think it's interesting what you say about the stick. I feel that the arched recession in the wall of the back room of Celosia's place might be a door and I've tried several things like shining sword beams through it and exploding arrows and even getting celosia to ram into it by standing Wander in front of it. Nothing worked of couse. What it is is the tall arch with a round carving above it. Whenever you see one of these round carvings in a wall, it is always above a passageway or door. That's why I think this is a blocked off door. Anyway, I never tried backing Celosia into it using the flaming stick. Not sure if there would be enough time....
i find this thread very interesting for a number of reasons:
1) i always found it strange that in the regular game (not time attack stuff) celosia's fight is the only time you're given an extra tool. - the stick - and you use it only for that fight. i often thought if there were a secret the stick would be a good route to it.
2) i also found it odd that nowhere else in the game is there fire burning besides celosia's arena and barba's. seeing the fire in barba's basically begs you to bring the stick from celosia's arena to barba's. (which the game will allow you to do BTW) the only reason i haven't tried it is because last time i was in barba's arena i tried to climb up to the fire and realized i couldn't get close enough to light the stick even if i had it.
3) in ICO, sticks of flame are used all the time to open doors.
all these things put together make this one of the best secret theories i've seen.