If you own it then just frame in a drywall wall to cover the whole wall, and finish however you like. You could leave a hidden access door on the one side to hide stuff in if you wanted.

If you rent then you could hang a wall of drapery across that whole wall you could build a cornice or just rods or wires on the ceiling. From fancy to rustic you can go any direction with this:

if you did not want to cover the whole wall you could just focus on the bed...

Thanks these are great ideas! We do own it, so we have more options.