How I do the corridor:
There's 13 potential spots on each barrier line. One can only be seen if you have Circle of Transparency active.
Make sure that there's only one or two Ignis around, not close to you, and cast an RC between you and them, where the RC won't kill itself running into a barrier trying to get to the monster. If there's 3 or more, have them chase you around the lava pool and invis when you get more than a screen away from them. Keep running the same direction to circle back to the corridor. Recast the RC as needed.
Start at one end (I start usually with the south side, where the one that you need the CoT to see), try to step one step into the barrier. If you take damage (about 20 points damage with 70-75 resists), step once to the side, and try the next. When you get to about 50-60 health, stop and heal before getting the next. When you find the safe way, mark it with a bandage or coin, then go through and repeat the process on the next barrier. Hopefully, you'll get to the point where most of the ignis either respawn behind you and out of sight, or on the other side of the teleporter where they won't see you. Eventually, once you find the way through the last barrier, you can run through to the teleporter. Then, I go clean up any Ignis in the main room while waiting for my friends with the cores to drop.
Alternatively, you can have friends fight the Ignis the whole time, and casting to keep you healed as you feel your way through, and have them follow you through the marked squares, to keep protecting you.
As for spells to find your way through, I can only imagine casting summons onto the barrier lines, and seeing where they can walk through. I GUESS you could cast an EV or Blade Spirit on the other side of the line, attack it to make it try to get to you, then walk along the barrier as it chases you, until it finds a way through - but that seems unnecessarily dangerous, given there's deadly spawn around too, especially since you'll have to dispel it when it does make it to you. But I've not tried that.