The huge-sized cave was discovered in 1975. At this place the karst water of several cold and warm-water sources mix together. From here the mixed medicinal water goes further through a narrow corridor, and then steadily it gets - at 38,5 °C temperature- from the underwater-cave to the thermal lake. The underwater-cave can be visited with just keeping the strict regulations and with the permission of the nature reserve competent authority. Of course, the regulations of cave-diving have to be obeyed to.
The living environment of the lake:
The living environment of the lake is unique deriving from the temperature of the water and its specific composition. The micro- organisms of the water and mud greatly contribute to the curative effect of the lake. The sulphur-bacteria obtain sulphur from the water; other bacterium families play an important role in decomposing the cellulose and forming the medicinal mud. In the world we can just find the "Micromonospora heviziensis" here, which greatly decomposes protein and cellulose. The living environment is so varied that some plant species only occur here in Hungary and even in Europe.
The most beautiful plant of the lake: the water-lily has become the symbol of Hévíz. This flower can be also seen in the coat-of-arms and flag of the town.
The red water-lily from India was domesticated by Sándor Lovassy in 1898 who was a teacher at the Economy Academy.
Due to domesticating tests, in the lake we can also find Egyptian blue and white water-lilies and also the lighter-coloured mutants of red water-lilies.
The indigenous white water-lily occurs rather in the water spout. The flowering of the strictly protected plants already begins at
the beginning of summer and it lasts till the end of November. The leaves of the water-lily brake the evaporation of the lake; the runners at the bottom of the lake protect the medicinal mud containing radium.
In the north, east and south the medicinal park with a Fenwood character can be visited just restrictedly and it is forbidden to leave the built-up walking path. Due to the impact between the lake and its protective forest a special local microclimate has formed. Because of watery areas the local climate is more balanced. Forests catch the winds and the lake and its environment is often covered with vapour.
The western protective forest-which has been shaped by the Festetics family-consists of black pines, spruces and larch-trees. The dominant species of the lower crown level are the following: robinia, ailanthus and the different versions of
maple. The more than one hundred years old hornbeam trees evoke the past.
The wine-growing has a long tradition in Egregy, which belongs to Hévíz. Wine-growing had been domesticated by the Romans, which was further cultivated by the Hungarians as we can see the traces of it in a document dated 1221 in the Árpád era. The medieval village was destroyed in the Turkish era and in order to supply the number of inhabitants at the beginning of the XVIII.th century, German settlers moved to Egregy. Similar to their ancestors they have learnt traditional wine-producing in the region of Lake Balaton. The wine-hill of Egregy was declared to be a place, where quality wine is produced in 1998. The different types of wine were pronounced to be wines with the character of the Balaton Region.