From a structural standpoint, we're looking at building an overgrown deck with a few modifications thrown in for safety, since unlike the builders of a real castle, we don't want anyone to actually get hurt attacking it. For example, the perimeter walls are only six feet high to the front, and two and a half feet high in the back. An actual dunn would be higher, but there's a lot of difference between falling from six feet and falling from a height of eight or ten feet. Other safety modifications aren't as apparent. For example, the castle gates will be barred with a 1x4 instead of an actual beam. That way, half a dozen burly fighters acting in concert can bust open the gates and enter the castle without doing permanent damage to either themselves or the gate.
Another safety feature is visible in the side view. We'll be excavating dirt from in front of the wall in order to create a moat-like feature, and then using that dirt around to the back of the wall to create a sloping ram that will protect anyone falling off of the deck towards the inside of the dunn. If you're looking at the dimensions of the lumber used to build the deck and thinking, "That's a lot of over-kill," you'd be correct. We're intentionally using heavier structural lumber than would be called for in any ordinary deck and fence, partially because we want this to look substantial, and partially because it needs to be substantial. Even though it's not really a castle wall, it will be subjected to a good deal of force when an army of soldiers collides with it, and we want it to stand up to the stress of blow after blow, year after year. The deck over the castle gate is actually the trickiest part structurally. It will perform the function of a command center when the castle is being attacked, and a viewing platform when armies are fighting in front of the castle. Another function of the deck that it's obvious from the drawings is that the supports for it wil form a tunnel to trap incomming fighters. When the gate is forced open, invading fighters will find themselves in a twelve foot long tunnel they'll have to fight their way through before they gain access to the center of the dunn.
The interior view of the deck shows another safety feature, landings on the stairway. Wearing a helmet really limits a person's depth perception and balance, so we're especially concerned that the stairs be as safe as possible. One way to prevent someone from tumbling down a flight of stairs is to break them up into short sections with a landing at the foot of each section. That way, if a person trips they can only fall a foot or two and aren't at risk of tumbling down head over heels.