This is a sea cliff at Suweolbong Tuff Ring, on the western edge of Jeju and near the end of Olle 12. Jeju was certified as a Global Geopark by UNESCO in 2010, and nine sites were nominated as geosites as part of that; Suweolbong is one of them.
Borrowing some words from the “Suweolbong, Hill of Winds” guide book, a tuff ring is formed by hydro-volcanic activity, i.e. molten lava comes into contact with water (in this case, the sea). A tuff ring is distinguished from a tuff cone, which is relatively tall and steep, the difference being due to the relative viscosity of the molten rocks.
The layers in these photos are a result of pyroclastic flow, the same mechanism that destroyed Pompeii. Layers of volcanic material flow downhill to give the stratified effect. In addition, fallout from the volcano drops onto the layers – hence the embedded larger rocks and the sags in the layers.
Follow that with the action of the sea to create the cliff and you get this remarkable coastline. Living on Jeju is like living in a text book of physical geography.