Dia is 5 km long and 3 km wide and covers an area about 12 sq km, extending from west to east. North of the Dia, there are two islets with gulls, Paximadi and Petalidi. In the southern part of the island there are 4 quiet bays: the gulf of St George, which is the only port of the island, the Gulf of Kapari, the bay of Panagia and the Gulf of Agrielia. On the east, there is the Gulf of Aginara. The island has a maximum height of 220 meters and the landscape is generally characterized by stones and shrubs. There are areas with rocky cliffs that reach 60 meters.
Dia played an important role in navigation during antiquity, particularly in Minoan and Medieval times. For the precocious seamen that sailed in the open Cretan Seas, it constituted the best possible natural "signal", indicating the approach of the Cretan coast with its natural harbours, while at the same time it helped in the anchoring of the ships, effectively blocking the strong northern winds. During Minoan times the island was populated and, near the bay of Agios Georgios, a harbour settlement was established.
The Undersea discoveries of Jacques Yves Cousteau in 1974-5, while searching for the lost Atlantis between Crete and Santorini, with a special bathyscape, are of great ecological and archeological interest, as seven wrecks were found on Dia. In 1976, Cousteau discovered some squared and rectangular rocks in the seabed that made up an artificial breakwater, which researchers named Cyclopean Walls. Cousteau suggested that there stood one of the biggest and most important ports in the whole island of Crete. The harbour appeared to have sunk due to the destruction caused in the 1450 BC volcano of Santorini. However, the port was later found to be much older, thus research became more complicated.
Detailed aerial photos also pointed out traces of settlements, confirming the hypothesis that the island was previously inhabited. However, more archeological research in the area is deemed vital for further establishing the evidence found so far.
The island had a small area were vine was grown up by fishermen, till 1937.
According to the legend the island was created by Zeus: Zeus, while he was dominating the world from his throne in Olympus, he looked to his birthplace, Crete. He was surprised to see his Cretans hunting with bows and spears, wiping out his beloved wild goats (kri kri). The goats were children of Amaltheia the goat that nurtured Zeus with milk while he was hiding from his father Cronus in Diktaion Antron Cave. He got that angry, that he decided to kill all Cretans. Immediately, he blew a lightning into the sea and a huge monster emerged to destroy the Cretans. However, the other gods tried to make him change his mind, but in vain. Then, Poseidon, the god of Sea, said to Zeus: "My Father and King, how can you devastate Kourites? Is that the way to repay the good that they have made to you?". Kourites were Cretans that were banging loudly on their shields when Zeus was crying, so as not to be heard by his father Cronus, who would eat Zeus. Zeus immediately changed his mind. Then he took two pieces of rusk and threw them towards Crete. So, when the monster tried to eat them, Zeus with a thunderbolt petrified the dragon with the rusks. This is how Dia and the two islets of Paximadi and Petalidi were born. Also, according to legend, Theseus, after killing the Minotaur, escaped to Dia with Ariadne.
The island is a very important refuge for native plants and animals with very small dispersion in the southern Aegean and one of the most important areas were falcons nest (Falco eleanorae). On the island, you may see many wild rabbits and hares coming out from the bushes.
Scientists believe that 5000 years ago the island was full of forests, and many springs. However, the forest has disappeared because the wood was used to build ships, while after about 1000 years springs stopped as well. Also, the island is a shelter for the endangered Cretan Ibex.
On the island there are no facilities except a tavern at the port, in the bay of St. George. Here, there is the beautiful church of Analipsis (Ascension of Christ), from where you can observe Crete and Heraklion Gulf. Moreover, from the port starts a stone paved path leading to the north of the island, to the forestry shelter, and another that leads to Analipsis Chapel. Next to the chapel, there is the main shelter, where you can stay overnight (no electricity), after contacting the port Office of Heraklion. If you don’t have your own boat, there are boats offering daily tours to Dia. They start from the port of Gouves, Hersonissos and Heraklion.