The right drawing with only red walls is the original foundation of the house. When the previous owners made an extension, they also expanded the basement to have all the sewage pipes there. Previously, there was only a toilet with a shower in the basement, which is why the extension was done to have a toilet and shower on the ground floor.
I need to remove the small piece of the old wall to place stairs to the basement. There is already one, but it turns and twists a little at the beginning and end like an L staircase. I would like to have a straight staircase there.
The middle drawing is what it looks like now, and the left drawing is what it looks like now.
The house is old and there is no detailed drawing. We've renovated quite a bit in the house, and now we're at the last stage with the basement and stairs.