Ai no Shuku (間の宿, mid-station) were unofficial post stations along historical routes in Japan.[1][2] These post stations formed organically along routes (such as the Tōkaidō and the Nakasendō) when the distance between two places was too far or when there were difficult passes nearby. Because they were not officially designated rest areas, travelers along the roads were not allowed to stay in these post stations. Sometimes the Japanese is shortened to 間宿.