Ft. St. Catherine
Fort St. Catherine is one of the largest(if not the largest) fort in Bermuda. By the 1940's there were around 100 forts on the island, but I think St. Catherine is one of the most impressive.
The original fort was built in 1614 by Governor Richard Moor. In 1973 it was strengthened by Andrew Durnford. Later in the 1820's and 1840's it was changed some more. By this time it was the physically imposing monstrosity you see today. However, again in the late 1800s more large guns were mounted at the fort.
Originally the fort was meant to defend against the Spanish who had made some claim to the island in the 1500's, long before the British landed there. Then later the French and the new United States of America became threats. Finally it was used during WWII as a training ground.
Today, you can tour the fort for a small price. I'd recommend it. I think there's a guided tour if you chose it. Otherwise, there are a few displays throughout the fort. These include replicas of the Crown Jewels, as well as military clothing and arms. And of course, you can see the huge guns mounted about the fort.
I didn't visit the fort this year, so I don't have any really good pictures. The St. George's Club golf card(See the Golf Club page) has a decent aerial view.