Underking Castle Day 5 Door Closed

I have been following Grogor Walkthrough to get through the castle, but i get stuck at the part where i have to open three doors to make my way up to the Sword of ages and beyond. I cannot get past through the last door after which there is a lever on the right bottom corner that opens the door to the room with a hole.

Any idea how i can open this specific door? is it a bug or i have missed a lever some where?

I know this is a old game but still i would like some help if possible!

Please help someone!

I don't remmember the exact location and the Underking castle was large and was whole lot of pain. But try using Barreta if possible. She have the skill to spot secret levers and something like this.