Old sulfur mine (Milos)
Decades ago, sulphur was mined, processed and shipped in the steep, deep-cut valley. Although the entire installation with its buildings, machines and loading gear has been heavily eroded by the ravages of time, astoundingly it still sits undisturbed in the landscape as a ghostly industrial ruin. At the far end of the valley there are numerous galleries that were dug into the hillsides.
For reasons of safety the mine and galleries can no longer be entered.
Source: http://milos-greece.com/en/sulphur-mine.html