Vines or other plants if you get any natural light in the room, and you should fix the plant holders to the shelf or wall if you can put plants

It's a really problematic space for a shelf. You definitely don't want anything up there electrrical, or anything you might use while bathing so you're not tempted to half-stand up in the tub to get it and slip. You don't want anything that if it fell into the tub could get ruined (paper, baskets, etc) or break dangerously (glass) or hurt you if heavy.

If you are unwilling to remove the shelf maybe lining up a long supply of shampoos or bubble baths in plastic containers. Any decor objects you add you should find a way to secure to the shelf.

I'd take the shelf down and put some art there instead--looks like something a stager probably put for appearance, but I think the ledge behind the tub would work for bubble bath, etc., and the shelf isn't super useful in its current location. You could also try using the tub with the shelf and see if you find you need it first--if you keep it, I'd use it for soap/shampoo/etc. but be aware that it will get gunky if it's wood. You could potentially line it with shelf liner first to help. I'm guessing this bath also has a shower, though, so this tub may be used primarily for soaking and less for actual washing--in that case, the ledge should be plenty sufficient and you can take the shelf down.

(Or actually--maybe a towel rod? Unless there's one nearby out of frame? I'd want one within reach of the tub.)

Is the function of this shelf purely decorative? If so, I’d lower it a few inches, add a clock off center, maybe a rectangular piece (mirror, picture) to counteract the circular clock and candles of varying heights to give a spa like feel with a splash of greenery somewhere in there.
If it’s meant to be more functional, I don’t think that’s the correct shelf for that space.

A shelf? Really?

Why is there a shelf?

I wouldn't replace the shelf with compliated decor that will be complicated to keep clean because it doesn't look easy to reach over or around the tub to keep things clean.

Maybe you should be ultra minimalist and get one of those shelf figurines

;)

or grow an orchid

be sure to secure the bottom of the pot to the shelf or wall

Maybe just one Fornasetti plate (or as many as you can afford -- I think there are 8)

https://www.svenskttenn.com/us/en/range/table-setting/plates-bowls/plates/plate-fornasetti/105421/

The shelf looks strange there. I would go with gorgeous art that is soothing, like a warm soak in a beautiful tub.

Ideas

I’d lower so as to make it practical, less awkward and if you strip and stain the same color as your floors, it will feeel less random and build on this look (see below).

I’d remove that shelf.

There are better options, but I don’t have any idea what styles you like, what the rest of the room looks like, what your needs are (storage?), etc. More context would be helpful.

ETA: Regardless of what’s on that wall, I like having a stool or chair nearby my own tub. Looks like you have room for one.

How about a more functional shelf on the wall to the right? And stool. :)

Take it down.

The straight edge of the shelf is jarring - it doesn't go with the pretty lines of the tub. BeverlyFla has some beautiful ideas - decor that will complement the tub lines. That's the direction I would go....especially if you already have to purchase items to put on the shelf.

“The straight edge of the shelf is jarring...”

That was my first thought. I agree with the suggestions of art.

Fwiw I think most of wall decor ideas suggested here will look like junk.

@mytwocents do you have any other ideas? I took the shelf down , what do you think of a towel rod along that wall

Is there a towel bar nearby right now? If not I think I'd put a towel bar or hook on the wall at the bottom of the tub and art on the side wall (just based on where the lighting is).

that looks like a fireplace mantel, not a shelf above a tub. it's too clunky.

something like this, lowered, looks much better.

Or, to protect the wall you really should have a wainscot or tile

you could do a simple matte subway tile, something like this, w/the wood shelf and some art

another one showing tile (ignore window) maybe a leaning towel ladder, wood stool, art. I like the ledge idea though. see below

You could do a whole lot to update that tub area and make it look really nice.

really like this look too. I like the wrap around ledge too.

greenery, mirror wall art, shiplap

I like this too w/the vertical planking, the art, some natural/textured items and a low ledge

this too. maybe a similar light (flushmount may have to do w/your height) the basket, stool, the marble ledge behind the tub, vase/stem/twigs

A natural wood shelf would look nicer and bring in some warmth.

you have room for something like this too

inset a niche w/shelves in the wall. do some type of wall treatment

this is a cool wrap around shelf w/some art if you want a vintage feel

beadboard is a nice touch too

Morgan, can you post other sides of the room?

What decor styles do you like?