The Peter and Paul Fortress, located on Zayachy Island, is a historic fortress founded by Peter the Great in 1706. It originally served a military purpose but evolved into a notorious prison where political prisoners faced harsh conditions. Among its famous inmates was the Decembrist leader Sergei Trubetskoy, who was imprisoned for his role in the failed Decembrist revolt against the tsar. The fortress is also home to the Peter and Paul Cathedral, which houses the tombs of nearly all Russian emperors since Peter the Great, adding a layer of royal drama to its already haunting history. Visitors often report feelings of unease when touring the dungeons, suggesting the lingering spirits of the political prisoners still haunt its walls.