PROSPECT, Maine — The observatory high atop the Penobscot Narrows Bridge has opened for the season, giving the public 360-degree views of the Penobscot Bay islands, surrounding towns and even Mount Katahdin.

State officials say the observatory, which opened Friday, is the only one of its kind in the United States.

The glassed-in observation deck is 420 feet high on top of the western tower of the $84 million Penobscot Narrows Bridge that links Prospect and Verona Island over the Penobscot River. The bridge replaced the deteriorating Waldo-Hancock Bridge and opened to traffic in December 2006.

On clear days, visitors can see as far away as Mount Katahdin and Monhegan Island.