You should use them as inspiration not try to copy what you see ... Use one of your road textures, use textures from Texturelib for moss, grass, stones, gravel, create a texture that's going to be blended in SFML with your road texture.

Two textures, one with a stony ground, one with grass, I used overlay on the grass one, added a layer, cloud render the grass texture and changed the alpha channel to blend them together. It has taken a mere 3 minutes start to finish ... The snowy/icy winter texture and the water texture, all I did was adding two color layers, connected the cloud render textures and blend them. C'est aussi simple que cela!

Thanks for the images and the explanation. I tried google to understand what cloud rendering may be and found out that this is a kind of online service to create textures!?
I understand how this blending works but I don´t fully understand how I could implement this in my game to make the road textures more interesting? The goal is that in the end there are many slightly different tiles. So I could use many slightly different textures to blend on the road texture? Is this what you suggest?

Sorry for causing a misunderstanding! Render->Clouds is what it is called in paint .NET used to create the examples. It's Perlin Noise

What I suggest is that you are going to create a texture atlas in which you put your ground tiles plus any new textures to make the ground tiles look slightly different and blend them together. You could also simply store a number of ground plus altered textures for roads, paths, caves ... This could speed up the whole process. You'd still have to alpha-blend any of the resulting textures into the surroundings to make it look good. For reference take another look at one of my posts in the German forum where I showed you an example of it. In your program you would only need to write a small texture/sprite selector to use them.

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Okay, I have a texture atlas with all the paths and roads and the different geometries. Of course it is no problem to paint variants, but it is difficult to create beautiful variants of the tiles. There I notice again how I reach my limits as a pixel artist ;-) ! With cobblestones, grass or stones placed on top always look strange. So far I had best success with holes (missing stones) or with darkening of single stones etc.!

I have also been working a lot with normal mapping lately and I might implement it in the caves. You can achieve great effects with it (especially in dark environments).

So I see ... Don't lock yourself into what you believe is pixel art ... Well you got some pixel objects like the lamppost in there, the goat is cartoon/comic style, the trees and plants are lifelike and your ground could be pixel or simple tiled and a mix of cartoon graphics. Since it's the ground textures you are working on now, decide on an art style matching your trees and plants and underlying grass textures. Make them match and work from there with one that's easy to change and adapt. I would strongly suggest you start studying 2d art styles and find a good match. If it's still just the ground/cave/indoor textures you are going to change then that's fine as long as they match, match, match!

These are a lot of good tips. Thank you. For the moment, however, I'm more interested in the lighting system and am in the process of integrating normal mapping into the game. It's especially nice in the caves and creates a denser atmosphere there.
The different graphic styles are still a work in progress, even though I like some of them. For example, I think it makes sense to design the world of people and the world of nature in different graphic styles. I like this idea and it fits into the story as a whole. Other things, like the roads and paths, I'm tackling bit by bit.
Thirdly, I am slowly working on the continuation of the story and creating concepts for it.

I think in 2-3 weeks I will have finished the normal mapping and can present a new version of the game :-) !

Glad to hear back from you! It's been a while now. :)

I must really say your dedication is admirable. Whatever you are going to work on now or next just make sure to get it done at your own pace no need stressing anything now. :-)

One aspect I thought about which I feel could add to your game is environmental natural sounds. A river or brook for instance, the squishing of feet when it rains, a thunderstorm, snow crackling, wind, rustling trees, dripping water in caves. The latter should not only be heard but also seen of course. The water running down slowly from stalactites and onto stalagmites.

There are many sites offering those free of charge though I think being a developer you should like to support and buy them. Shouldn't cost you more than Euro 20 to get quite a number of sound effects. Just something to consider. :-)

When I work a lot on the game I often don't feel like writing in the forums and so there is less to read from me ;-) !

About your ideas: There are already a lot of ambient sounds in the game, which are selected according to the environment (swamp/trees/fire/water/cave and weather and also season). Of course, they don't appear in the videos because there is background music. On the subject of normal mapping, I will also release a small trailer "In the Caves" and maybe I can include a few silent moments where you can hear the wind howling or the water drops in the caves :-) !

The idea with the stalagmites and the water sounds interesting. Such a small animation would be easy to integrate.