For my environment I chose the themes of fantasy and decay, because when I tried to come up with different environment concepts for the different theme combinations many of the ideas fell into the fantasy and decay ideas.
While I did eventually choose the fantasy and decay themes I thought of ideas for different environments.
Theme ideas
Some examples of this are: for beauty and fantasy, I thought of a mystical garden with a glowing blue tree in the centre, a small pond, with a bridge that goes over it, taking you to a central island with a hole in the tree that leads to a small room that looks like a home or more specifically a living room.
Another idea for this theme combination is a mystical forest filled with flowers and vibrant organisms leading to an opening with a small wooden pavilion that has good views of the whole forest and is covered in fairy lights or similar small lights that give a mystical ambiance to the area and a small pond.
For fantasy and corruption I immediately thought of the corruption from terraria, as it is an unnatural colour and spreads thorough the world over time and creates mutated creatures. However I believed that anything, I try to create with this in mind would be too similar to the terraria corruption and I did not want to just copy my environment.
For science fiction and alien I thought of an acidic, green and grey or brown planet with a green atmosphere and strange landscape, this could be a cool environment to make but I did not feel that I would be able to properly display the jagged and strange environment that I had imagined.
For horror and utopia I thought of seemingly a beautiful utopia from the outside that looks pristine and happy, then when you enter it is dark. Corrupted with blood trails inside the buildings and signs of people trying to escape. There are no signs of such a struggle or escape attempt on the outside.
Final theme choice
After thinking of environments for several different theme combinations, I decided on making a desert with ruins full of mythical forces, that seem mystical, magical and unknown. With an altar surrounded by cliffs and a cave and a tomb or a tunnel with an altar inside.
After deciding on the themes I liked, I started to think of ideas of what to have in the environment, eventually I decided on a circular platform with broken stone pillars sticking up and a pedestal with a floating book on top. With a temple or cave in the cliffs nearby, in an otherwise desolate mountain valley.
When thinking about the overall environment I decided that a rocky and mountainous desert would be the best choice. Since ruins in a desert would be a interesting environment to create. That I could make more mystical by adding runes and environmental details that imply the mysticism of the area.
For the ruins aspect I want them to were to appear to be mystical in comparison to the valley in which they are set. I wanted the environment to be a secluded and mysterious set of ruins that uses the secluded environment to make the location seem mysterious but not impossible. For example, a gap in the mountains that the sun is perched in. A perfectly circular space in a mountain range with a circular set of ruins and an altar with a book that seems in pristine condition despite the decay around and even on the pillar upon which it sits.
For the indoors environment, I originally decided to make a cave or tunnel in the side of a cliff. I thought about a regular cave but I felt that it would not match the mystic theme. Therefore at this stage I chose a form of crypt or tomb that matched the theme better. Since it would be an underground or even a building, built into the side of a cliff. With this I could add more mysticism to the environment with subtle runes placed around and a mystic glow to the caves that helps reinforce the fantasy aspect.
After more thought and playing around with different ideas I decided to change my indoors environment to a temple that is embedded into a cliff face, with this I could add extra detail to the whole environment, including the outdoors section as it adds more interest in the otherwise desolate desert.
With my final concept I could also create a more grandiose environment than I could with a mountain cave. Since it has more area to work with. As temple buildings are normally large and spacious. Whereas a cave or catacomb are cramped and tight. Also a cave would be much darker and make it difficult to add the same details and mystic elements that I could add with a temple.