Saiho-ji has a nickname that tells the whole story: Kokedera, the moss temple. The garden is carpeted by well over a hundred varieties of moss, in shades from emerald to near yellow, spreading between the trees and around the pond in a soft, damp quilt, and a day of rain makes it glow. The effect is accidental in origin, since the moss spread after the temple was neglected in the nineteenth century, but it fits the garden's older bones, which were laid out in the fourteenth century by the Zen master Muso Soseki. Muso also designed the garden of Tenryu-ji, on the other side of the Katsura river, and you can see a family likeness.
The temple is run with great care, and the price of that care is that you cannot simply turn up. Visits require a reservation made in advance, and visitors take part in a short session of sutra copying before walking the garden, with a donation expected. This keeps the numbers low and the atmosphere calm, a very different feeling from the crowded temples in the middle of the city. If you plan a ride around it, sort out the booking first, since slots may fill up, and arrive on time.
The surrounding district, Matsuo, has other things to explore if you have time. Matsuo Taisha, a short distance away, is the shrine to the god of sake brewing, and brewers from across Japan come to pray here. The hills above are wooded and calm, and a stream runs through the shrine grounds. In general this western edge of Kyoto is a quiet residential area, with narrow lanes, bicycles, and the occasional old farmhouse hiding behind a wall.
From here the ride goes to Yakushi-ji, in the south of Nara, across the Kyoto basin and then over the low hills near Uji. It is a steady, mostly flat day, and there is no need to hurry. Roads around Saiho-ji are tight, and parking is limited, so a smaller bike is easier to handle. Fuel stations are along the main roads to the south and east, and the area has small bakeries and noodle shops for lunch. Visit in the rainy season of early summer if you want the moss at its richest, or in the golden light of late autumn, when the maples set the green on fire.