The Penobscot Narrows Bridge and Observatory is the very first observation tower constructed on a bridge in the US. Opened in 2006, it is also the tallest public bridge observatory in the planet with its tower measuring a total of 447 feet in height. The bridge itself is of the cable-stayed designed, crossing the Penobscot River.

The Penobscot Narrows Bridge was a replacement to the Waldo-Hancock Bridge that was built in 1931. It used a mix of epoxy coated steel and carbon fiber for the strands, which also makes it the first construction of the sort to use such materials.

When visiting the Penobscot Narrows Bridge and Observatory, visitors would need to pass through Fort Knox Historic Site and are required to pay a small entrance fee that already covers the observatory and access to the historic site.