Took a ride to check this monster out...what a beast! It is definitely worth paying the $5.00per person to go up and look out the observatory. Here are some facts I found online.
• It is the world’s tallest bridge observatory, reaching 440 feet to the top plus another 10 feet for the antenna. It is one of only four bridge observatories in the world, with others located in China, Thailand and Slovakia.
The Penobscot Narrows Bridge offers a view of Fort Knox, foreground, and Bucksport in background from its observatory. JANE ANDREWS
• There is an unobstructed 360-degree view of the Penobscot River, Bucksport, Fort Knox and Penobscot Bay and even the mountains on a clear day through its 9/16-inch-thick glass walls.
• The $85 million structure has already won nine awards for design and engineering.
Interesting bridge, i whish more had lookout towers :)
There is also a bridge with a tower/gate in prague, it's the Charles bridge.
It's well known in europe because it's a very old bidge and a landmark of Prague.
It's at one end of the bridge though, not at the center, and not THAT tall.
http://en.wikipedia.org/wiki/Charles_Bridge