Niji-no-Matsubara, stretching along the Karatsu Bay coastline, is designated as a national scenic beauty spot and is considered one of the three greatest pine forests of Japan together with Miho-no-Matsubara and Ama-no-Hashidate. Niji-no-Matsubara is approximately 5 km in length, 1 km wide and made up of around 1 million Japanese Black Pine trees. Its history dates back as far as the beginning of the 17th century when Hirotaka Terasawa, the first lord of the Karatsu domain, started planting pine trees on the dunes along the coastline for protection against the wind and tide. Niji-no-Matsubara is also famous as a place surrounded in seven mysterious legends, which are described below.
- Cicadas do not cry in the area because Hideyoshi Toyotomi is said to have once scolded cicadas which were being noisy.
- The pine trees are all short. This is also believed to be due to Hideyoshi glaring at a tall pine and saying "You are haughty".
- Only the Japanese Black Pine species grows here.
- There are no snakes. This is said to due to a wish by Suwa Princess who is worshipped at Suwa Shrine.
- There were two trees with identical branch arrangement. Only one of these remains standing today.
- The water in the well at two tea houses near the sea is fresh water.
- The extension of the line connecting Takashima and Kashiwa Island is the middle of the pine forest.