Ses Fonts Ufanes

Found in the middle of the forest in Campanet, Spain, the Ses Fonts Ufanes is a unique hydrological wonder that only appears after heavy rainfall, like some sort of mythical natural legend. 

The little river looks like it just appears up out of the ground, but it is actually a sort of overflow spout from a nearby river. With heavy rains, the river tends to swell, filling an underground chamber until it overflows, creating the natural font. All of this activity takes place underground, however, so to the naked eye, the appears that the spring river simply pops up out of nowhere. 

The water issues forth from the ground at a pace of around one to three cubic meters, covering the rocks and ground cover beneath its waters. The site can only be reached after a 15 minute walk through the woods, making it a well hidden marvel.

However the phenomenon is not completely unknown. In fact it has been marked as a contemporary UNESCO site, earning all the protections that affords. In addition, the property that the disappearing water flow sits on was purchased by the government in 2005, so that could better keep an eye on it. At least when it hasn't vanished completely.