Shlisselburg Fortress an old Russian fortress on Orekhovy Island, at the Neva`s headwaters on Lake Ladoga ,35 kilometers east of St. Petersburg. The fortress is UNESCO World Heritage Site. (As part of the Swedish Empire, the fortress was known as Nöteborg (`Nut-fortress`) in Swedish or Pähkinälinna in Finnish, and became the center of the north-Ingrian Nöteborg county (slottslän)).