Don't know about the rest of that side of the room, but you could even convert it into a cover/ bookcase combination.

I like radiator covers. We have them throughout our older house.

D John Design's solution has worked perfectly for me for 44 years. You have the same problem I had. My radiator controls are high enough that a built-in cover would interfere with the window sills, as would yours, and I dislike the pipe coming out of the floor. I had misgivings about making the covers backless and stand-alone, but they have proven quite sturdy and also can be easily moved for cleaning. I had steel perforated panels cut to size by a metal fabricator, and chose knot-free lumber, thinking that would best survive the periodic steam heating and cooling. I made three of them in two days using hand tools and simple butt joints, fastening them together with L-braces and screws, not nails. They've never needed repair.

First of all, to cover it, you need to see how long you can run your cover (otherwise you end up with an ugly box). All the examples extend both sides to the walls. Does this work in your place.Secondly, what is the rest of your style? Industrial chic/grunge would indicate painting it a bright colour that makes it a feature - and that is a lovely radiator to highlight. (Be careful to choose the right paint though). Traditional style means painting it a light or similar colour to the wall.Also as you have an air conditioning unit by the window, anything you do, won't really work in the summer or warm months as the air conditioning unit would need to be "disguised" or made less apparent. Perhaps the bright radiator might help in this case?

I don't have style yet. I am just starting the renovation. This is the room (living room). I am thinking to have curtains covering the AC...

We helped one remodeling guy to do small painting jobs. We painted the radiator in high gloss black. In thermodynamics, black objects radiate and absorb heat better

Will curtains near the radiator pose a fire hazard ?

Working on the same principal, some houses use radiators that run behind the baseboard so there's no bulky radiator. The baseboard was metal and had vents.

if you have the room, i would build that out into a bookcase, as linked up above.
i think it would look lovely.

Search the box above under Photos for rad cover and you'll be inspired. In winter, remove the air unit from the window and store it in a closet.

Our advice - cover! We covered and it looks gorgeous. Check out etsy.com for sources, too.

Thanks everyone! We ended up leaving it as is... Just painted the same color as new walls and covered with the curtains. Works fine:) the box would take too much space....