Really regret not making it to Saihoji (Moss Temple) despite having a reservation. It's one of Kyoto's most exclusive temple experiences - you can't just walk in like other temples, you need to book ahead and participate in Buddhist activities like sutra copying before they let you into that famous moss garden.
The pictures I've seen of those 120 different types of moss creating this ethereal green carpet are stunning. While it's definitely not a kid-friendly spot (children under 13 years old are not allowed to visit, except on Children's Day), it seems like the perfect place for solo contemplation. The fact that they limit visitors and require participation in spiritual activities probably creates a completely different atmosphere from Kyoto's more touristy temples.