The buildings, including the oldest reinforced concrete apartment building (No.30) were already time-worn, and had reached the end of their usual life -about 60 years- when the mine was closed. But while people were still living on the island, they were kept in a usable condition, at least outwardly, through daily maintenance and continuous repairs. When the mine was closed and the island was abandoned, these buildings were left without maintenance and were left to collapse because of weathering. As a result, it has been possible to make a comparative study of the weathering process under conditions rarely observed in a normal urban setting. The weathering process of a reinforced concrete building depends upon such conditions as its location and environment, the quality of the original workmanship, the suitability of the materials used in its construction, and the quality of maintenance. Natural conditions are terribly severe on Gunkanjima, and therefore the effects of weathering are so obvious that the whole island constitutes a vast natural laboratory for studying the deterioration of buildings. In this chapter, our purpose is to shed light on some of the technological problems which arose at the dawn of modern Japanese architecture by a study of the weathering process and to collect information which may be relevant to the future development of building technology. Phenomena which had passed unnoticed while the island was inhabited, manifested once it was deserted and, conversely, highlighted the quality and quantity of maintenance which the buildings had required. These phenomena provide us with important material for understanding the nature of this community in its high density environment.