There is not exactly some natural place in Delhi. You have some options like Garden of Five Senses, Ladu Sarai and Deer Park, Haus Khaz Village but they are always overcrowded and you may witness some activities like pre-wedding shoots and a lot of PDA which sort of affect the natural aura of the place. But they worth visiting if you are okay with these things. A better alternative will be Bonta Park located near Civil Lines. It is somewhat less crowded and more thrilling when it comes to terrain. You can easily sight some monkeys and variety of birds and enjoy the nature.