What about shelving or turn it into a linen/storage cabinet?

Something along the lines of this

Something like this in a compatible color. https://www.houzz.com/products/46-natural-fiber-chest-of-drawers-on-wheels-mocha-prvw-vr~9404972

If you have the money have a cupboard built in. If you want a cheaper alternative then a large storage basket on the floor and shelving above.

I'm digging the tall white cabinet. Where is that from?

http://www.homedecorators.com/p/hampton-bay-6-door-tall-cabinet/

http://www.homedepot.com/p/Home-Decorators-Collection-Hampton-Harbor-25-in-W-x-14-in-D-x-72-in-H-Linen-Storage-Cabinet-with-6-Doors-in-White-7784660410/203104029

HI -- Seems odd to me that extra space is in a powder room. Almost looks like it could have been for a shower or possibly a stacked laundry pair . But because it is a powder room you can make it extra special and do something different from the rest of the house . Putting a linen cabinet in as suggested if you need the storage . You usually don't really need much storage for linens in a powder room . Another idea would be to have a pretty little makeup table and a cute chair and a fancy mirror and lamps . Also using a dramatic wall paper would really show off the room and make it fabulous !!

it was an extra shower space.

An opportunity for something creative (art) and a lighting element. An unexpected visual element. Powder rooms usually are there for guests and for you in day-to-day mode, do something out of the box, have fun and you can never go wrong with color.

I'm loving the ocd of that comment!

I would trick this powder room out for sure!! First I would paint the walls a great smashing color. Then I would put a tall very ornate mirror in that spot at the back and a little velvet bench in front of it. There are so many ideas floating around in my head for fun things in this room. Let me post some exotic ones! It is really basically boring beige right now!

You could paint it this dark blue and then find cute antique prints and frame them like these and put them in that cubby maybe even a little table like the one here inside it rather than a bench. Some candle sconces would be great. It would be so fun! A big great full length mirror too.

This would be interesting--pricey though but it is the concept. You can hunt antique shops for tall pier mirrors. They are hard to find, but not impossible and antique shops have been struggling in the past several years so you might get a bargain. If you wanted to go more English here is a cute one.You could put a small bench in front of this.

Have fun with it and make it eclectic and a conversation piece. Your women friends will love it, and men won't understand it. haha!

Snow Leopard rug?