The only bridge observatory in the United States is opening for the season this weekend in Maine, offering 360-degree views of the Penobscot Bay islands, surrounding towns and even Mount Katahdin. The Penobscot Narrows Bridge Observatory opens for its seventh season on Saturday. The sightseeing tower is high on top of the western tower of the Penobscot Narrows Bridge that links Prospect and Verona Island over the Penobscot River. This year’s opening was delayed because of the demolition of the old Waldo-Hancock Bridge, which was shut down when the Penobscot Narrows Bridge opened in December 2006. The 42-story-high observatory is open from 9 a.m. to 5 p.m. until June 30. It’ll be open until 6 p.m. between July 1 and Aug. 31.