What are you planning to store there?

Is it a cold air return? If so, you can probably get any furniture piece you like, pulled out far enough from the wall to allow for air flow behind it. Put blocks on the floor to keep the furniture at the correct distance.

This location calls for a furniture piece. I would prefer a low boy / credenza but an interesting taller case piece could work. Typically built ins aren’t on tall large, and built ins don’t work against a stair. That’s unless you want a floating credenza which could be awesome.

A cabinet with doors or drawers on legs should work for the space.

What are you looking to store at this particular location? Would be helpful to know so that practical pieces can be suggested. There are no other locations that can be considered for your storage needs?

No there aren't any other locations on that floor - we are maxed out, and bc back of house is modern open floor plan we are very limited. We wanted to used this area for paper towel storage, toilet paper, napkins, soap refills, etc. When looking at all the credenza and chest recommendations I have photo shopped them in and they look really odd. Maybe I will talk to a carpenter and see if we can come up with sleek floating cabinetry since nothing I am storing there will be heavy. Having a credenza sitting off the wall looks awkward as well since space is limited and you can see the gap going up the steps and walking into the bathroom. Depth there is 26 inches.

Blueberry, it looks like a small storage unit in the powder room against the wall under the window & with a floor vent in front of it. What about a custom built in either on both sides of sink or a single unit spanning the space on sides & under the sink? it could stop at sink apron bottom height or go up to sink & have a door to access the pipe. It could be fronted / finished with the same style beadboard as the stair walls around the bench. Seems like a custom build should work there - it could have short legs or not so no floor damage done either. If it had legs & was custom built it could be lifted out of place to work on any plumbing issues.

I feel like anything you put there will look odd and may cover the beautiful spindles or block air flow. I would think about adding storage somewhere else, like maybe adding organizers to closets or garage? This looks like a beautiful house btw!

I can be off here, but I've seen several instances where others turn that stairway area into recessed storage in the wall. Could a couple of deep drawers or one large cubby door be built into the wall above that vent?

Is it possible to have the vent moved to the floor? Would take a consult with an HVAC guy, but might be worth it,, then you could have a built-in put in under the stairs.

What do you need to store ? How about a bench with storage under the top , I do think the art is a bit odd there . I like a spot to sit to put on shoes or boots

I agree with Hallett and Co. that the space needs a piece of furniture and not cabinets. Our first house had a very small kitchen, and the previous owners had squeezed a breakfast bar in, with cabinets below the counter, hanging above the baseboard radiators. It looked very, very odd, but was useful storage, and hidden under the counter overhang.

I've seen a fair amount of case furniture from the 1920's that sits up on legs. Not the short, stubby legs that have been shown, but tall, graceful legs that would easily get the storage part above the vent. Tall legs reappeared in Midcentury Modern. Given the space restrictions, you are probably looking at something custom/semi-custom so it fits, but you could search 'sofa tables with storage' and see if anything jumps out. Sofa tables tend to have legs.

I also vote for freestanding furniture up on high legs. Maybe get a piece built but definitely don’t do a wall hung unit there.

That's a great unit and I would do something like that if I could find the dimensions. The tricky part is having the legs be 12" high because our air return is right there. Between that and finding dimensions that are too wide, too tall, wrong color, or legs are way too short.