This is Fort Mississauga, located in Niagara-on-the-Lake, Ontario, with the Niagara River on one side of it and Lake Ontario on another. Located just across the river from the USA's (much bigger, much older, and much prettier) Fort Niagara, Fort Mississauga was built hastily during the War of 1812 and kept manned until 1826. It was re-manned during the Upper Canada Rebellion (1837), the American Civil War (precautionary measure in case the fighting spread, I guess), and the Fenian raids. It was used for training at various times during the 20th century wars as well... but little Fort Mississauga has never actually been attacked.
It's a Parks Canada site these days, and it's the only example of a star-shaped earthwork in the country (you can see the beginnings of two star arms on either side of the gate). Although it's conserved to some extent (walls stabilized, etc), it isn't staffed or restored like many of the other historic forts that are still around. One more fun fact about Fort Mississauga-- it's situated right in the middle of North America's oldest golf course!
