I am on chapter 10 and I have been wandering around underground for a day..

This part drove me nuts, too. The red and blue things will drain the water from behind those doors that say the pressure is too high to open them.

The very simple way of getting back out of the underground passage is to go back to where you dropped down (I think it's the first left as you walk away from the balance room/save point). Run along the left wall, then the wall straight ahead, then jump to the landing you originally jumped down from. Be sure you have found the insect key. Go back up the stairs to the larger door (in the hallway with the dead ninja). Use the key to open the insect door after you fight the blue and pinkish monsters. Fight the giant worm, obtain the new electricity power, and, I think this is where you get it, the red thing to drain the water. Once you go back and drain the water, you can open the smaller door in the hall with the dead ninja. This room gives you the other little statue to open the door with the earth statue in front of it. This will eventually lead you to TWO giant worms. There you're on your own, 'cause this is where I am!