Seven Foot Knoll Lighthouse, Inner Harbor - Baltimore, MD by Sam R on Flickr.
Via Flickr:
Built in 1856, the Seven Foot Knoll Lighthouse is the oldest “screwpile” lighthouse in Maryland. It was built on cast iron pilings with corkscrew-like bases screwed into the soft mud on the bottom of the Bay, eliminating the need for masonry foundation. The lighthouse marked the entrance to Baltimore’s harbor for 133 years before being moved to the Inner Harbor and restored. Taken from: www.baygateways.net/general.cfm?id=59