The miracle of Lourdes is one of the best known in modern times and is recognized as a genuine series of miraculous events by the Catholic Church and the Pope recently visited the sight on the 150th anniversary.
    In 1858, in a grotto near Lourdes, France, Bernadette Soubirous, a fourteen year old peasant girl, had a vision in which a female figure appeared  to her.  She originally reported it as simply a small women, but after talking to the priest, it was determined that she was speaking to St. Mary, mother of Jesus.  Bernadette saw the lady seventeen more times.  It was not until the third appearance that the vision spoke.  On each subsequent appearance, more people were present.  Only Bernadette actually saw Mary or heard what she said, but others witnessed some other events that occurred their.  I'm not going to list all the details, they are available on a number of web sites.  I'll just mention the most important.  
    On the ninth visit, Bernadette was told to go drink and wash at the fountain.  She saw no fountain, but went to the cave .  Still seeing nothing, she turned back to the apparition who then told her to go in under the rock.  Inside she found a small puddle.  Bernadette dug into the mud and was able to get a small amount of water clean enough to drink.  Eventually, a spring did began to flow there and the water is believed to have brought about a number of miraculous cures.
    An interesting fact I learned recently.  This site may have been known as a holy place long before the appearances to Bernadette.  Some ancient cave art was found in the cave in the grotto.  Since many experts now believe that ancient cave art was mostly done by tribal shaman, usually to record visions they had at the sight, the shaman may have considered that cave a holy place thousands of years ago, which, in my opinion, adds credence to the Catholic belief that it's a holy place, though they may not see it that way.