Japan's engineers have long challenged the difficult geography of valleys and mountains. The Mukaiyama Tunnel was dug in the 1940's, and is a monument to ongoing development of travel infrastructure in this area. The newer Kyōei Tunnel was dug under it in the 1970's, leaving the older Mukaiyama tunnel's exit on top of the new one. The end result looks like a "double tunnel", and has come to be known as a unique monument to the Yoro Valley's development, and literally an "underground" sightseeing spot.
176 Kuzufuji, Otaki Town, Isumigun
(4 mintutes by car from Yorokeikoku Station on the Kominato Railway)