The Ryōan-ji garden is considered one of the finest surviving examples of kare-sansui ("dry landscape"), a refined type of Japanese Zen temple garden design, generally featuring distinctive larger rock formations arranged amidst a sweep of smooth pebbles (small, carefully selected polished river rocks) raked into linear patterns that facilitate meditation. (Thank you Wikipedia, couldn’t have explained it better, or ‘at all’).
The temple and its gardens are listed as a UNESCO World Heritage Site. The site is one of the 17 Historic Monuments of Ancient Kyoto. Kinkaku-ji(the Golden Pavilion) is also one of these Kyoto monuments.
The stamp on the left is issued by the Department of Tiny Stamps.