Thermal Lake © Heather Cowper
Lake Hévíz is the world's largest thermal lake, a most extraordinary sight with its huge milky blue surface covered in water lilies and steam. The warm water wells up from a volcanic crater spring about 40 metres (128ft) below the surface, with the recommended maximum time in the water during any session being one hour. The mud is said to be slightly radioactive and good for various medical conditions, but only in small doses. A pavilion in the centre is reached by a covered bridge, and indoor swimming takes place in an area enclosed with plexiglas. Gaps in the plastic lead to the rest of the lake where swimmers can float among the water lilies and swim between platforms bobbing on the surface. There are also various other spa and health treatments on offer.