When I visited Mitarai, we stayed in Hiroshima and on the next day, we headed to Yamaguchi City. It was not a walking / biking tour but I am going to make a post anyway.
1) Ruriko-ji Temple
We were traveling with a rented car and our first stop after Hiroshima was Ruriko-ji Temple in Yamaguchi City.
The five-storied pagoda, built in 1442 is a national treasure. It is lit up during the night (until 10pm) throughout the year.
Address: 7-1 Kozancho, Yamaguchi City, Yamaguchi Prefecture
Access: 30-minute walk or 5-minute drive from Yamaguchi Station of JR West
2) Joei-ji Temple
The next stop was Joei-ji, another temple in Yamaguchi City which was built about 500 years ago. The rock garden in this temple was designed by Sesshu who was a painter / landscape gardener / priest.
The website of Joei-ji is Japanese only but the photo gallery is worth seeing.
Address: 2001-1 Miyanoshimo, Yamaguchi City, Yamaguchi Prefecture
Access: 15-minute walk from Miyano Station of JR West
10-minute drive from Yamaguchi Station of JR West