This is so difficult to narrow down to 3. I guess I would say 1. Mountains - I'm very interested in places like Mt. Everest. 2. Marine life - My favorite animals are whales, dolphins, seals, etc. 3. The weather - I love how it turns from day to night and how the seasons change. I also love snow, rain, and wind.
I wanted to say space for one of my answers, but I guess that wouldn't be considered nature. Space is pretty damn intriguing to me. The sky, sun, moon, and other planets. The world is a pretty amazing place.