The cavern of Saint Trinity is located in southern Evia at the foot of mount Ohi and about 3km from the town of Karystos.The entrance to the cave is close to the church of Saint Trinity, at about 50m away from it and 20m higher. The place is full of large plane-trees that cover the small church in their shade. A ravine starts here and goes all the way to the sea. The place is beautiful and easily reached by car through an asphalt road which ends very near the church of Saint Trinity. To find the cavern entrance we follow a path that starts just above the church.
The cavern, which is well known by the locals, became more widely known in Greece after SPELEO organised numerous exploration missions. It has been formed by an underground river that is the source of the spring of Saint Trinity. The river flow rate is about 195m3/h and the water is high quality drinking water. There are more water springs around the mount Ohi and all of them have an all year round water flow.
The cavern has been known since the ancient times. Near the entance pottery shreds have been found. First contemporary report on the cavern is found in texts about the wider region of Karystos, by Karakostas and Gounaropoulos, in the first half of the 19th century. More precise information can be found in the book ‘Karystos’(1954) by C. Papamanolis, which contains information from the missions of 1932 and 1934.
There are some large and small ponds as the climb continues and many different colourful shapes and sizes of stalactites There is a third cavern also with stalactites and the floor is covered with stone from past rock falls. Only few cavers visited the upper parts of the cave and the old watercourse.
Exploration and new total mapping of previus and current visits. 950 meters of new passages in a total of 3150 meters of the cave were explored and mapped thanks to the efforts of the cave diving team that managed to pass more than eight siphons to complete the operations needed. This mission corrected and arranged all information from previous visits into one accurate report and map of all the cave.
Observations were made with regard to the fauna of the cavern, and bats were located in the big room of the cavern. They also found dolichopoda (Petrochilosi) and two species of guano feeding insects. Measurements of the ambient temperature were taken (15-16 °C) and analysis of the water quality was performed. It was found NH3 free. Using 400g of fluorescein, they proved that the water in the caverns is the source of the spring.