Besides the rocks with functional utility (paths, lanterns or islands), the most interesting are those called sute-ishi (which can be translated as "nameless" or "discarded rocks"). As their name suggests, these rocks seem to be dumped randomly, but of course, the randomness is the result of painstaking planning... One of the most famous garden where you can admire such sute-ishi is the Koraku-en in Okayama, photographed here...
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 22mm
Aperture: F/5.6
Shutter Speed: 1/800s
ISO Sensitivity: ISO 200