Read the Japanese version here.
Inuyama Castle (Inuyama-jou, 犬山城) is definitely an interesting place to put on your 'to see' list, if only for the beautiful view from the top.
The castle itself isn't very large, but is built on a hill and looks over the Kiso river, which separates Gifu from Akaike. It was a fortress at its inception (like most castles, I suppose), but now its a place of prayer. People come and leave prayer plaques (ofuda, お札), writing their wish for the New Year, etc on the back. If your wish is granted, you come back to give thanks. One we found read, I hope a healthy baby is born; another, I want to get into high school. I visited Kiyomizudera once, and left a plaque asking that my cousin in Afghanistan stay out of harm's way; it was granted, so I guess that means I should be going back soon!
Inuyama castle was built in the 1500's by an uncle of Noda Obunaga (yep, one of those 3 great unifiers of Japan that you've heard about in your world history classes. Did you know that all three of them were from around Nagoya?) It is one of 4 castles which are national treasures - it has never been reconstructed (it has been restored, though, as some parts were damaged after an earthquake). The walls are still natural, uncut stone, and the beams are wood, shaped without the aid of a plane. Its staircases are narrow and extremely steep, with thin steps. This is to slow down enemy intrusions, and also leave the enemy with only one hand, since the other would be occupied with pulling himself up by the handrails. Personally, I found going back down just as hard, if not harder, than going up. Other enemy-proofing areas of the castle include the room where rocks were kept for dropping on the invading samurai. The view is good as well: perfect for gazing over sparkling, sprawling towns, and beautiful mountains; and for shooting/throwing rocks down at your enemies.
Inside are several displays. One shows various samurai armors. The fanciest belonged to the high ranking members of the cavalry.
Another shows a killer whale statue which used to be on the roof. The shachi (鯱) is kind of like a protection against fires, which occurred often because of the materials used in construction (wood and paper which are, of course, pretty flammable). The reasoning behind it all: the killer whale is a large sea animal, and water beats fire, right?
And outside there's a six hundred year old tree. It was struck by lightning a few years back and killed, and now it's preserved as a sacrifice. There's quite a bit more to see than what I've explained, even though the castle isn't as big as some others, so I'd definitely recommend a trip to visit if you're ever in the neighborhood!