The Castillo de San Marcos is described as a heavily haunted site with numerous paranormal reports, including ghostly apparitions of soldiers, disembodied whispers, unexplained cold spots, and shadowy figures. Many claims focus on the spirits of former prisoners, like the lovers caught in a tragic tale of jealousy and discovery within the dungeon. Visitors also report unusual scents, such as the sweet smell of perfume. Visitors have seen apparitions, including Spanish soldiers and shadowy figures, particularly around the watchtower and battlements. Common reports include disembodied voices, whispers, and the metallic sound of armor or footsteps echoing through the fort's coquina walls. Guests have experienced unexpected drops in temperature, sudden chills, and the strong, sweet scent of perfume. Some report feeling an icy touch on their shoulder only to find no one there. A story tells of a jealous Colonel who discovered his wife's affair with a lieutenant. The lieutenant found two skeletons in a hollow part of the dungeon, and the spirits of the two lovers are said to be forever entwined. The fort is said to be haunted by the spirits of both soldiers who died on duty and prisoners who suffered and died within its walls. The fort has a history of conflict and was the site of attacks, particularly during the 1702 and 1740 sieges by the British. In addition to its role as a military fortification, the Castillo also served as a prison for Native Americans.