Cats moving into new place

Well two years after husband and I divorced cats stayed with him because they were used to the house and the environment.They were two years old at the moment, now four years old. Hubby' new housemates are very very allergic to cats. So the cats learned to get adapted to living outside in the garden and they even got a lovely house! They always wander around the backdoor though but they are happy enough. Now the allergies especially from the newborn baby are getting worse by the day.
So to make a long story short... I volunteered to have the cats back.
I have a nice garden and enough room.

I have one very important question...In my house the stairs are "open" just like a ladder.
Will and can a cat climb up these stairs or have they a natural fear of such things?
I want to put the litterbox upstairs because my living and kitchen area is one open space and I know from the past that the cats want to do their business in private...and who can blame them hÃ[emoji]169[/emoji]?

So can someone tell from experience if cats can climb an ladder?

Maybe a silly question but I want to know for sure.

Thanks in advance!

I'll move this to Behavior for you.

However, I do know that cats can climb regular ladders, so having open stairs shouldn't be much of a problem for them.