You might be thinking something different of course. So this scene will be outside. In this scene I chose day. I also I choose a land scene over water scene. I used stucci and mable as textures for the temple and a jpeg of dry mud for the floor.
Planes are very good for water, ground and mist.
Hit the tab button to get out of edit mode. Stretch it wide enough to enclose the scene's subject. My new plane is shown below in highlighted in blue below. Add a new material for the fog plane. By default you'll get a gray material with no texture.