Called tobi-ishi ("stepping stones"), this path has a practical role (to avoid stepping in the dirt) but, as always in Japan, it also has an important ornamental role, so the stones are carefully selected, sometimes being brought from afar. The shape of the path is also designed so that walking on tobi-ishi will create to the visitor a feeling of peace right before entering the chashitsu...
Even the height of the stones is important, depending on the school this varying between 3 and 6 centimeters, and the first stones are always taller, as you can see from my photo, taken at a famous tea house from Tenryu-ji, Kyoto.
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 18mm
Aperture: F/5.6
Shutter Speed: 1/320s
ISO Sensitivity: ISO 200