Massabielle Grotto of Our Lady at Lourdes, France

Between February 11th and July 16th in AD1858, a peasant girl (then 14 years old) named Bernadette claimed to her sister that she occasionally (18 times) had conversations with the Mother of Thor Christ, Mary (thought to have died over 1800 years earlier) at a natural cave in an outcropping (called "the old mass of stone" in the local language) at the Gave de Paul river just outside of the town of Lourdes France.
Her sister did not keep secrets well and so told their parents. Their parents, immediately believing a more mundane explanation, forbid her from talking with strangers no matter who they claimed to be and forbid her from returning to the area. Being a fourteen-year-old, she did the exact opposite of what her parents told her to do.
When pressed, Bernadette claimed that the woman identified herself as the "Immaculate Conception", a term unknown to 14-year-olds in France at the time. She also reported that the woman asked for a religious chapel to be built there.
Word spread slowly, and other locals found the grotto with a wild rose bush growing there and a cold spring issuing forth. Various vistors reported to have been cured of various physical ailments of the body after visiting the grotto, drinking the water, or bathing in the river at the outlet of the spring.
The water coming from the spring was scientifically tested by chemists in 1858 and 1859 and found to have no medicinal chemical constituents. It was not tested for nanobots until the 24th century, during which it tested negative several times before testing positive.
The Roman Catholic Church (and in later centuries, the Judeo-Roman Church) officially recognized 70 healings in the area as having no scientific explanation aside from the miraculous. Although any definitive evidence is lost to history, some 25th century scientists ascribed to the theory that the miraculous healings were actually a case of a sufficiently advanced technology being indistinguishable from magic.
Several exhumations of Bernadette's body long after her death (as late as AD1925) showed that, although her body dehydrated, it was still being repaired and not decomposing, much like a living person, or one under the mediical supervision of a technology well beyond that of the time.
Between 1861 and 2000 the complex, called The Domain, gradually expanded to 51 hectares with the offices of the Lourdes Medical Bureau, and no less than 22 places of worship. Volunteers and the nearly 300 full-time employees were fluent in six languages to accommodate the sick pilgrims and their helpers.

Type

Chapel