The Seven Foot Knoll lighthouse is one of the few screw-pile lighthouses remaining which once guided mariners along the waters of the Chesapeake Bay. These Lighthouses stood on top of metal legs which were literally "screwed" in to the sandy bottom of the bay. These lighthouses were extremely vulnerable to the storms and ice flows which are a common occurrence on the waters of the Chesapeake. The Seven Foot Knoll light was constructed in 1855, and houses a fourth-order Fresnel lens, which aided shipping into Baltimore's harbor. The station also housed a fog signal that was used during bad weather. The lighthouse was donated to the city of Baltimore, and in 1988, the structure was removed from its pilings and transported by barge to its current home on Pier 5 on Baltimore's Inner Harbor. Today, the lighthouse is open to the public, allowing visitors to step back in time to the days when lighthouses served as the most important aids to navigation.