I FINNALY figured it out.
Hers what you need:
Harry and Guu quest done. This is only my theory since that quest does nothing.
Unstable explosives. This is definitely important since in 33 Pd there’s ALOT of places you can see it would do something.
And:

Go to lv. 33 with the key and unstable explosives go to the pad. When you get there use the unstable explosives to go up the wall and place a bomb this will hopefully if my theory is right make the wall go away and then you will be able to go farther in the caverns.
I will be sending screen shot to explain farther.