The Snake Island or Saint Peter is an island in Prespa Lake and it's the largest island in the Republic of Macedonia. It has an elliptical shape, 750 m long and 450 m wide, with the highest part 50 m above the lake. The island "Golem Grad" is an extremely important area of the Galicica National Park due to several environmental phenomena. Two forest communities are clearly distinguished in the flora: the wild juniper forest and the forest of the wild almond and the European nettle tree. The great cormorant (Phalocrocorax carbo) and the Dalmatian pelican (Pelé-canus crispus) are present in the fauna. A characteristic feature of the island is that the dice snake and the common wall lizard are much larger than the inland populations, while the nose-horned vipers (Viperaammodytes) are dwarfed.
Several cultural and historical monuments are located on the island on a relatively small area. Apart from the preserved churches "St. Peter" and the medieval church "St. Dimitrija", there is also an Early-Christian basilica, where remains of a floor mosaic have been discovered.