This is a larger harbour fortress designed to provide a safe berth for merchant ships in particular.
Some might criticize that this fortress has too many cannons (whose instructions can be found on this page), but I am of the opinion that everyone can do that as he wants. Also the many levels might be a point of criticism, but again you can decide for yourself. For the battlements or the embrasures I was inspired by Fortress Dawnguard from The Elder Scrolls V: Skyrim (see DLC Dawnguard). The one or the other may have recognized the rough Pralelle, in this case a short applause.
The fortress is meant to protect the surrounding waters so that ships of all kinds can move around safely. However, there isn't much to shoot at in Minecraft, except maybe a few squid. Therefore, this fortress has mainly decorative value.
The large gate is primarily intended to provide space for transports (e.g. horse-drawn carts). An equally spacious tunnel leads to the actual port, where the transported goods can then be loaded onto a ship.
This room represents the audience hall of the knight or prince (again, be creative) who rules the fortress. The throne is perhaps not quite as well done, but you can optimise that too when building your own. And whoever discovers that there is an invisible secret passage behind the throne, which can be used for the possible escape of the knight or lord (even if this is not very honourable), will receive five euros from me...
A little joke on the side, whoever discovers an invisible secret passage is really damn good.
The two armor sticks... er brave warriors guarding the throne can also be found on this page. Who now says: "But armor stands can I just find in my inventory?", then pay attention to the fact that our brave warriors wear shiny polished swords. So now I ask: "Are the matching arms also in your inventory?
I am always open to suggestions for improvement, because no one is perfect and so is no build. This may sound overbearing, but I make this request simply because I am curious and I care a lot about improving my builds....