Trying to produce a convincing outdoor scene was the toughest project I have done so far. It taught me so much about using lighting properly. HDRI environment textures were the top learning point for this project.
HDRI textures map onto the background and act as 360 degree lighting. There are thousands of these freely available online. They are much easier to use then using classical 3 point lighting due to the thousands of separate light sources that a real sky produces.
When initially working with this scene the lighting was very unrealistic. It was very difficult to not flood the scene with significantly too much light or with a strongly prevailing colour. When the proper lighting was introduced, beautifully defined shadows could be created.
The other major learning experiences were with the modelling itself. I found that I could simplify many of the geometries a huge amount be mapping high resolution photographs instead of applying different single material textures. I imported some beautiful sculptures from around the world and framed the rest of the structures around them.
The nature in the background was particularly difficult to do. This is definitely worth revisiting when I have gotten better with natural scenes. Unfortunately I feel that the leaves and grass bring the realism of the scene down drastically. I have, however, bought some lovely tree models which might save me some time. These trees and bushes would take forever to model myself and bring very little to the scene, other than the impression of nature.