Jeju Volcanic Island and Lava Tubes

According with UNESCO this site "bears testimony to the history of the planet, its features and processes". Besides that, looks extremely beautiful 

Volcanic Island of Jeju

This postcard was sent from Sweden by Amina

Jeju, also known as Jejudo, is a volcanic island, 130 kilometers from the southern coast of the Korean Peninsula. The largest island and smallest province in South Korea, the island has a surface area of 1,846 square kilometers.

A central feature of Jeju is Hallasan, the tallest mountain in South Korea and a dormant volcano, which rises 1,950 meters above sea level. The main volcano includes 360 satellite volcanoes. Volcanic activity on Jeju began approximately in the Cretaceous and lasted until the early Tertiary period. The most recent eruptions are estimated to be about 5,000 years ago, which puts the volcano into the active classification, meaning eruptions in the last 10,000 years. - in: wikipedia