When decorating a bathroom, tiles are most often used. It's not about tradition, it's really comfortable material. Hygienic, not afraid of dampness, beautiful, durable. But this is not the only suitable material, nowadays there is something to decorate a bathroom with in addition to tiles.
Wallpaper
Paper ones are not suitable, they are short-lived in damp conditions. Acrylic and vinyl are better. When buying, we choose with the symbol "three waves" or a painted washing brush (moisture resistant), they are more stable. But still, the water resistance is insufficient: moisture penetrates at the joints and gradually renders it unusable. 
But these fit unambiguously. They are made like fabric, only the threads are made of glass. Special jacquard looms allow you to get a variety of surface patterns. 
Very solid coating, durable (last up to 30 years), environmentally friendly, non-flammable, does not require a perfect surface during application. Not afraid of fungi, dampness. Moreover, this wallpaper itself protects the walls from damage, so strong. Alas, the price is much higher than regular wallpaper, but it's worth it.
Do not confuse when applying: the inner and outer sides are similar, but there are differences. In rolls, the front side is wound inward, some manufacturers mark the outside with a colored stripe. A special glue is desirable. Fears of "harm" carried over from glass wool are silly and due to lack of information: these are completely different materials. After finishing the walls, such wallpapers can be left as they are, and can be painted, primed or decorated additionally - if desired, such wallpapers will decorate the bathroom with dignity.
Similar to wallpaper, but made of PVC foil, the glue has already been applied. Cheap, but requires very careful preparation of the walls before finishing, which increases the cost of the result. And you need to apply very carefully. And it's still unstable, sometimes it swells or peels off, so it doesn't paint the bathroom ...
In the video: assortment of PVC panels
Simple finish: 2 slats are reinforced, panels are alternately attached to them. Large selection, low cost, moisture resistance. In addition, they can cover pipes, cables, without obstructing access to them, even minor construction flaws of the walls. However, moisture condensation is possible between walls and panels. In addition, the material is fragile, dents or tears remain from impact (however, this damaged socket is easy to replace if you leave spare ones). Turn yellow over time. Another disadvantage: the availability and simplicity of the material determines its prevalence in public places. And the bathroom (by analogy) doesn't look chic enough ...
We can only talk about moisture-resistant drywall, the other is not suitable for decorating a bath... Cheap, easy to install, improves sound insulation. It is not particularly beautiful in itself, so subsequent painting is desirable. In addition, when installed, the volume of the bathroom decreases, and if it is already small ...
Mosaic
Time-consuming finishing, and artistic taste is also needed. But there is a wide choice, in principle, any drawing is possible. But, as far as maintenance is concerned, the tiles are simpler in this regard, there are fewer irregularities on them.
Stone, natural and artificial
Naturally expensive, so much so that for some it may be a disadvantage, not an advantage. The stone is heavy, which requires special care during installation. Better to hire a specialist. Marble (often it also means breccias, dolomite, carbonate mixtures) requires maintenance. Granite has a high hardness. The high price alone does not guarantee amazing results. For example, by completely finishing the bathroom with granite slabs, you can turn it into a kind of cave, and not at all chic ...
Reduces space, so poor choice for small rooms. Artificial is in many ways similar to natural, but much cheaper.
Wood
Not a bad choice. The material requires special impregnation, nevertheless it serves in dampness... You can gently burn the panels, soak them with a stain to develop the texture, which makes them more beautiful. It cheers up somewhere on a subconscious level, perhaps all of us in a past life are druids. Roads. Requires appropriate design in other bathroom elements (hangers, shelves, mirrors).
Slightly similar to conventional plaster in application - also a thick mass smeared on the wall. But only in the eyes of a layman, in fact, a special material. Very beautiful if done correctly. Nowadays, various types of such plaster are produced, so it's easy to choose what is beautiful for your concept. In addition, the "marbled" finish is very significantly different in cost from real marble. Clearly, in the direction of cheapness.
Painting
Perhaps one of the cheapest options for replacing tiles (although the price depends on the choice of paint), it is better to use latex paint - it is resistant to moisture. The result depends little on the method of application - any is suitable: with a brush, roller, spray. And strongly - from the artistic taste and skill of the performer. This is not a monochromatic painting, although any color can be chosen here. You can paint real pictures or use stencils. Alas, gray soviet walls bring only despondency ...
Original ideas for replacing tiles
Pieces of glass can be used. If there is access to orphaned material, for example, acquaintances work in the installation of double-glazed windows (and the owners have nowhere to put the old windows, they ask to take them). The installation and sale of plastic Salamander windows in Ukraine is carried out by the OKna5 company. You can get acquainted with detailed information about the company and questions of interest by following the link to the official website http://okna-kiev.com.ua/okna-salamander/
Cut the same pieces with a glass cutter and use them instead of tiles. You can also use mirrors. True, amalgam is afraid of dampness, besides, care is needed: the mirror also reflects dust, with the same pollution it seems more soiled. A combination is possible: use the wall as a canvas, and after painting a picture, cover it with glass.
So, as mentioned at the beginning, in order to decorate a bathroom with something other than tiles, there are a variety of ways to decorate the walls. In any case, it is not only (not even so much) efforts and money that are important, but artistic taste. However, we do not live on a desert island: it is not difficult to find free consultants or hire a designer. The second method is safer, but more expensive.