The island of Sado-ga-shima is 35km of the coast of Honshu, facing Niigata.
It is one of Japan's largest minor islands and served as an exile place for important figures since mediaeval times.
Emperor Juntoku (1197-1242), Buddhist priest Nichiren (1222-1282) and a Noh player Zeami (1363-1443) were all banished to Sado.
In 1601, gold was found at Aikawa, on the West side of the island, which startled a small gold-rush. Sado acting as a penal colony, prisoners were made to work as slaves in the freezing gold mines, a practice which continued until the end of WWII, when POW's and Korean workers were made to toil for the benefit of zaibatsu such as Mitsubishi, which owned the mines.
The Sado Kinzan Gold Mine in Aikawa (相川) has tours for visitors, as well as an adjacent museum.
Shukunegi (宿根木) on the south-west corner of Sado, is a laid back fishing village. There, you will find the Ogi Folk Museum, which is relatively interesting for its collection of (not so) old objects, such as ceramics, dolls, clocks, tools or radios.
There are also some temples and shrines scattered on the island. But you don't want to come here for specific sights...
The main reason to come to Sado is for its remoteness, rocky coastline and natural scenery, small fishing villages and an easy-going pace of life contrasting with metropolis like Tokyo.
How to get there
Ferries and faster hydrofoils operated by Sado Kisen run several times a day between Niigata and Ryotsu, on the east coast of the island, or from Naotsu (south-west of Niigata) to Ogi (south-west of the island).
Note that winter is best avoided for its harsh weather and the fact that most hotels are closed and transportation is rather limited.