Ryoanji temple was originally a country house of the Tokudaiji Clan, it was acquired in 1450 by Katsumoto Hosokawa for use as a Zen training temple. This temple was registered as a World Heritage Site in 1994.
When you enter the temple, check first how the rock garden is and how many rocks you can see. The model garden is just before the actual rock garden. The number of rocks is 15.
The rectangular Zen garden is made from only 15 rocks and white gravels.