Macro photography opens up a whole new world of amazing nature with details the naked eyes cannot see. It is often beyond imagination and stunning. To capture more details, you need high magnifications. Most dedicated macro lenses can achieve 1:1 life size magnification (subject and image on the sensor has the same size) without any accessories. If you cannot afford them, reverse-mounting a lens with short focal length (<~50mm) is a good alternative. Check out these great examples and how it is done.
With dedicated macro lens, you have fully functional auto-focus and metering. With a reverse-mounted lens, you may not have either. It can become difficult and frustrating at beginning. Practice will make it easier and reward you with great photos without spending a fortune.
For in-depth information on alternative macro photography methods, please visit this Nikonlinks page.