I have a floor plan of the Munsters house and it has the passage under the staircase leading to the dungeon also.

sounds good.

you mean the one in the opening credits? I am not sure maybe an old Universal employee or historian may know

Speaking of staircases, what was up with that staircase going down that was accessed by a hidden passage under the stairs going up? Where did that go to exactly? Not the dungeon as that was accessed by a trap door elsewhere. I always thought it was so cool how the staircase flipped up to reveal it though!
And he rubbed the pot roast all over his chest, excitable boy, they all said

In many older homes there were two staircases. The large one was for the family and the rear kitchen staircases were for the servants.

I recall a few episodes in which they were used, but it seems rare.
I always liked houses with two stairways.
Me too.
And he rubbed the pot roast all over his chest, excitable boy, they all said

I always liked houses with two stairways. It made it easier to get upstairs.

I just watched "A Visit from the Teacher." Eddie comes down the rear staircase into the kitchen, pausing to talk to Lily. This is a bit unusual for Eddie, as his typical route to the kitchen is via the cupboards.
As for the attic stairs, I believe they are actually located in Eddie's room. In the episode "Eddie's Brother," Herman visits Eddie in his room. Eddie is seen playing with Woof-Woof on what clearly appears to be the bottom few steps of a staircase. Since Eddie's room is on the second floor, it makes sense that these steps would lead to the attic.

I do think I remember Herman using it once now thta I think about it. Also, where were the stairs taht lead to the attic?

That was pretty strange.

In fact did they EVER use the staircase in the kitchen? I don't recall them ever using it.
Most people see things that are and ask "why?", I dream things that never were and ask, "why not?"