I have a few possible ideas I could use for the theme of my project. My initial idea was a Limbo type theme, a place between life and death where everything would be dark, with an emphasis on the lack of knowledge and heavily influenced by shadows and the lack of light.
The second idea was a hell theme, pools of lava flowing amongst walls of dark brimstone highlighting the entire level in a red glow. The lava acts as a very dangerous obstacle for the play to get by, and could help design some mechanics for the maze as well as the levels themselves.
Another one was a theme that would purposefully be scary or creepy, maybe disturbing. The theme would have an emphasis on death and decay, with skeletons lying around and strange things appearing in the vision or hearing sudden distant noises. Insects could be a strong part of the theme, emphasising the death aspect of the theme.
The final theme, and the one I decided to use is a plant based theme, with vines and roots overgrowing much of the environment, with large trunks jutting out of the ground.