Wallpaper or paint in the bathroom?

If you absolutely want to leave the old tiles on, I would not want to work with wallpaper. Here, I would find the better solution to use a moisture-resistant plaster. Note that the tiles must be very carefully cleaned of grease, dust, and dirt, you have to fill the joints (there are special fillers for this), and a primer must be applied. I took the liberty of sending you a link for your reference, where you can take a look.

Take off the tiles and plaster with lime-cement.

It is a hell of a job but it is worth it. I know what I am talking about. If a tile underneath ever loosens in the coming years, all your work will have been for nothing.

Therefore: Always do it properly.

Hello RaumFrei,

unfortunately, I don't see a floor plan or any photos.

Wallpaper / paint should also match entirely. Therefore, a photo from which I cannot judge whether it fits for you.

We have tiles "below" as a splash guard, although I would not have done it differently out of habit as a sitting pee-er.

You at least see a mix of patterned wallpaper, textured wallpaper, tiles, and glass / mirror. Maybe some inspiration for you.

Since it is a guest bathroom - and not a guest WC - I would not use wallpaper. It gets damp when showering and the glue will come off...

So maybe the "evil" but elaborate way with plaster and, for example, latex with contrasting color or also a glass wall with / without picture (doesn't cost much more than the wall version). Also available with LED backlighting.

Best regards
Jens

I am a big fan of tiles & color.

I would remove the old tiles. There are special tile chisels for that. It works very well with them without much force. The old tiles are basically lifted off with them. Everything else is probably just as laborious and in the end only shoddy work that you regret. I would plaster the rest as usual and install tiles where you like. We also tiled halfway up at our place and plastered the rest. And painted the plaster white. The wall tiles are light beige and the floor tiles are sand/mud-colored.