I recently watched Nausicaä of the Valley of the Wind and the whole film was visually beautiful and covered important themes dealing with war, compassion, nature, and other significant topics.
The plot involves a post-apocalyptic future where the last remaining humans are struggling to survive on a planet (supposedly earth but it's never directly addressed) that is progressively being taken over by vast toxic jungles that are full of giant insects and noxious fumes and materials. Humans cannot enter the jungles without wearing protective masks that stop the toxic spores from entering their lungs. The viewer is led to believe that the jungles are vile places and everything in them is hazardous. If the fumes are consumed for prolonged periods of time, they can lead to serious sickness and death.
There is one particular scene that stood out to me because it was very moving. About half way through the film, it's revealed that the protagonist (Princess Nausicaä) has been collecting spores and roots from the jungle and bringing them back to her home. In the basement of the castle she lives in, she has planted all the spores and has grown a miniature jungle. However, this jungle is not poisonous in any way and is actually beneficial for the air and the environment around it. It's not toxic because Nausicaä has been using pure water and soil to grow the plants. It's such a beautiful scene because it covers an important theme. Often times, something (or someone) can turn dangerous or destructive because of the kinds of things it is exposed to or absorbs. A person can become "toxic" if they grow up in a harmful environment devoid of any positive influence. A pristine life-giving river can turn poisonous if a factory dumps chemicals in it. Clouds can create acid rain if they are full of evaporated pollutants. There are numerous other examples of this phenomenon and the film portrays this issue in a richly vivid manner. This scene is also powerful because it pushes the viewer to reevaluate and question his assumptions about harmful things and consider important questions about the root causes behind something that is considered destructive or "evil."
Besides this particularly powerful scene, there are many others issues covered in the film in equally superb ways. I highly recommend watching it.