Geologically speaking, many lava tunnels and caves are characteristic geomorphic features in Che-Ju Island. Especially, cave-ins are found along cliffs of shoreline and streams. The prehistoric early inhabitants in the island used the tunnels and cave-ins as their major shelters from palaeolithic period to the iron period (AD300-600). These tunnel-dwelling sites and rock-shelters are unsidered to be long-term shelters from the palaeolithic period to the neolithic period. However, these shelters and sites might be changed as temporary camping sites from the bronze to the iron period.