Yeah, shelf the wallpaper idea.
If you cannot surround the upper half of the room with beams to lay a floor above for storage or a room accessible from somewhere upstairs, then do something visual to occupy the space from being bare.
Perhaps put mouldings around the room at a height of 9' and use paint to create a cozy effect. Paint is the single most least expensive element in a room that offers a lot of decorating impact. Select two colors that are on the same paint chip. Paint one color above and below the moulding line.
With 20' high ceilings, you should avoid "ceiling" or "pendant" lighting as they will just collect dust and cob webs. So, "can" lighting (recessed lighting) may work well high above, along with wall sconce lighting below that you can reach.
You may want to consider a dropped ceiling for energy efficiency reasons and to keep the humidity controlled if you are not planning on installing a ventilation system.
Whatever you put up high in that area, it will have to be maintained, whether it be a light or moulding or a fan vent to dust, so make it accessible.