Hallway 3 ' wide,12 ' long,don't need it, what to do with this space?

Well, what does the hallway connect? Bedrooms, bathroom, public space, kitchen? Without the hallway, how would you get through the house?

You did not say what was on either side of the "hallway" space, but it is at all possible to cut into the wall on either side, I would make this previously un unused and inacessible space into a storage area.

Cut an opening wide enough for sliding doors, install shelving before re-installing the doors.

It's got to be running next to some room. Take out a wall if you can, or make an archway. But if it is not connecting any rooms, build narrow shelves on the long walls and wide shelves at one end, and use it as a pantry, Christmas closet, tool room, unseasonal clothing closet, or library overflow storeroom. Best wishes 😇

Wow! If it was my "wasted space", I'd turn it into a neat little closet - of sorts. No. 1. You can never have too many closets, and No. 2. You wouldn't even need doors, just shelves and dividers. Have fun creating!

I have the almost exact same space .. my husband and I made picture ledges from scratch about 6' long ( 2 of them ) to display all our family photos .Looks nice but doesn't take up too much space since it's only 3' wide

We have an 80's home with no storage...it had a similar hallway leading to the master bedroom. We blocked the hallway off with drywall, changed the doorway to the bedroom to a different wall and turned that space into a walk-in closet for the master.

Storage

Closet

I like the idea of storage. Like so many have replied, you can never have enough storage. The other thought that popped into my mind is to turn the area into a reading nook, or cozy corner. Paint the walls a welcoming, relaxing color, put a comfortable chair in there along with a footstool, side table for your coffee, wall or table lamp, a small soft carpet, cozy blankets. Who doesn't love a nice, quiet cubby? That's not just a kid thing! :)

can go around the hallway, it connects main door to kitchen

good idea!