People bathe in a Bulgarian mud "spa" as heatwave hits Europe Every summer thousands of people visit a mud-and-lye "spa" on the edge of an open-air salt factory near Bulgaria's Black Sea city of Burgas. They spend time relaxing and floating in the thick lye, which is a product of salt-extraction that is so concentrated that it makes you float and is known for relieving bone and muscle pain. People then apply healing mud on their skin, which is said to have a positive effect on people's peripheral nervous system. When the mud dries they wash it off in the lye basins or take a dip in the sea. IMAGES AND SOUNDBITES