The castle of Virtsu belonged to vassals of the feudal state Bishopric of Ösel-Wiek - Western part of nowadays Estonia as well as part of Saaremaa and part of Hiiumaa. It was built in 1430 by Uexküll noble family and destroyed already in 16th century. Now the ruined walls are few metres high, but it really looks that there is almost nothing. That's because grass and bush is growing on the ruins.
Reference: Virtual Tourist
The Citadelle of Quebec is an active military installation and official residence of both the Canadian monarch and the Governor General of Canada. It is located atop Cap Diamant, adjoining the Plains of Abraham in Quebec City. The citadel is the oldest military building in Canada, and forms part of the fortifications of Quebec City, which is one of only two cities in North America still surrounded by fortifications, the other being Campeche, Mexico.
The first fortifications in Quebec were built by the Governor General of New France Louis de Buade, and completed just in time for the Battle of Quebec in 1690.
After the British conquest in the second half of the 18th century, the problem of Quebec City's defences grew more acute.