I haven't played ninja gaiden for a while, but I started playing again yesterday in the middle of chapter 11. Im standing in the high cave where I beat the big monster skeleton before. Do I go down, into the water? Do I go up? Please, can anyone help a little lost ninja?

Wow dude, how the hell did you get way back there? You have to go back down into the Aquaducts (ch.10 area), and go to the room where you defeated the final boss of that level, and go through the big door that the final boss of ch.10 first appeared in front of. Once you go through that door be prepared to do alot of swimming.

Well thats what I did. I defeated the big bidlike monster, went thru the biggie biggie door, did a LOT of swimming and found the underwater weapon and the oxygen thing, and at the end of the long swim there was a crack in the floor which led to the cave where the dinoskeleton was

Down where the dino skeleton is there will be a huge hole in the wall at the bottom of the room, just swim around the bottom of the room until you find it. Swim on into the hole and it'll lead you to the end of the level. Note: when you come to the open area with alot of those big fishies and the elevator that leads to the Monastery, don't take that elevator, swim down the path in the bottom-right corner of the area, when you surface there will be a save point and an elevator, make sure you save before you take that elevator up.