Wat Samphran Temple, Bangkok, Thailand. Jorge Macedo Photography. Hard to find the history of this mysterious building but semi-abandonned at one point & lacking maintenance due to past reputation (this link has some info & lots of great photos). Monks are welcoming but some parts are not open to the public.
The Chapel of Panagia Makrini in Samos - is built within a cave, probably some time during the 10th century and was added onto through the years. Inside the cave human bones were discovered and it's suspected that they probably belonged to those who resided there. The chapel was part of a larger monastery and according to Patriarchal Sigillion from 1816, it belonged to the Monastery of Saint George Sinai in Monidrion of Kastania.