Akiyoshidai is one of the largest Karst hills located in Miya city, Yamaguchi prefecture. It is about 16km x 6km square meters.It is registered as a special nature monument of Japan. This field was created about 350 million years ago as a coral-reef. There is an entrance to Akiyoshi Cave at the observatory. There are shops and restaurants at the observatory. There is also a strolling train from the observatory.