Niji no Matsubara is a long pine grove planted along Karatsu Bay to protect the coast from wind and tides. The trees run for roughly 4.5 km, making a shaded, slightly salty walk beside the beach.
It is counted among Japan's famous pine groves, but it is not a manicured garden. Its appeal is the rhythm of trunks, sand, road, and sea, especially if you pair it with the castle view from across the bay.