Curonian Spit National Park

Curonian Spit National Park covers the Russian-owned southern 41 km of the 98 km long, curved Curonian Spit – a type of depositional sandbar. The spit separates the salt-water Baltic Sea from the freshwater Curonian Lagoon to the east. The southern portion of the spit lies within Zelenogradsky District in Kaliningrad Oblast, Russia; the northern portion lies within southwestern Lithuania. It is a UNESCO World Heritage Site shared by the two countries.
The foundations of the spit were created about 15,000 BCE as the receding glaciers left the Baltic Sea behind, and the sand dunes of the Curonian built on the glacial moraine. The actions of sea and wind build large dunes, which average 35 meters on the spit. The area is one of high biodiversity due to the many different ecological communities in close proximity to each other: beach, dune ridge, wetlands of various types, meadows and forests. The Curonian Spit is the second longest spit in the world, after the 110-km long Arabat Spit in the Sea of Azov. The park follows the spit from the Sambian Peninsula in the south to the border with Lithuania about 40 km north; its width varies from 0.4 to 4 km. The water in the lagoon averages 3.7 meters in depth, and the water level of the lagoon is about 12 cm above that of the Baltic.

Wikipedia