Great Sand Beach, Sandy beach in Greece.

Great Sand Beach, also called Golden Sand, lies southwest of the fishing village of Marmari on Evia. Its shoreline runs about 250 metres and can reach 60 metres wide, with a large circline line inside the sea surrounded by rocks, trees and scattered houses. The beach changes shape each year with waves, winds and water, forming small lagoons; a smaller south-facing beach often appears on its west side.

The sources record no ancient harbor or trade history for this beach. Its documented past is tied to the fishing village of Marmari in southern Evia, and to the Petalioi Gulf, whose nine private islands face the shore. In 2020 the beach appeared in the Greek tourism ministry's advertisement built on the line that Greek summer is more than sun and sea.

Locals also call the beach "Golden Sand", while the official Greek name is Megali Ammos. European sports magazines have presented it as a prime spot for sea-sport lovers, and it featured in the Greek tourism ministry's 2020 campaign with the slogan "Greek summer is not only sun and sea, it's more than that".

The beach is easy to reach with several access points along the shore and parking available nearby. It is best visited during the warmer months when facilities are open and the water is comfortable for swimming.

The beach changes shape every year with the direction of waves, winds and water, forming small lagoons on its surface. A Venturi effect between Evia and the Petalioi islands means the sea is calm only when the south wind blows or there is no wind; when the north wind blows, swimming far from shore becomes dangerous, especially for young children.