Ahh, Siege. We all know it, some of us love it, others not so much. But I'm not here to debate the actual balance or gameplay on the map; I'll leave that to a different topic someone can make. Instead, I want to take a moment to analyze the centerpiece of the map: the castle. Is it realistic? What kind of castle is it? Does it resemble any in real life? Can we estimate when it may have been built in-universe?
Well, that's what I'm here to determine! Let's start from the top with a bird's eye view:
Right off the bat, we can see that this deviates from the "typical" castle design. There's no towers present, nor is there an obvious gatehouse. We only have one outer wall with a few bastions attached to a central keep. The bailey also appears to have been heavily dug into, which may or may not have been done during the height of the castle existing? The main reason it's hard for me to tell is because the trench actually opens into the undercroft (at least partially). The tunnels where the Ore Trucks go were clearly dug out long after the height of the castle's life, so we can ignore them.
Honestly, those tunnels and the presence of the ore could tell us why this castle is here in the first place. After all, castles were built as defensive structures first, so it's entirely possible that this one was built specifically to guard a rich mine. It's likely that the mine was so rich (or an enemy attack was so swift) that parts of it were left untouched by the time the castle fell into disrepair. All it would take is a curious prospector to discover that this location has a lot more left to offer, and suddenly the Allies and Soviets have great reason to fight over it.
One more noticeable detail is the fact that the wall isn't flush with the shoreline. This could tell us quite a bit about the history, as most castles built on or near water ways would generally line up the walls with the shore to minimize the possibility of enemies bringing soldiers or siege equipment up against the outer wall. For reference, let's look at Bodiam Castle:
As you can see, the castle is surrounded by water, but the water appears to have receded over time. Indeed, this may be exactly the case with the castle on Siege; perhaps at one point, the walls were, indeed, flush with the shore, but the water level went down over the centuries. It's likely that the land bridges to either base on the map are fairly recent and would have been shallows back in the castle's heyday.
Now that we're done looking at the outer wall, let's move into the keep.
Looking at the keep itself, we can see that this isn't the typical keep design. The Donjon has fallen, and appears to have been built in the middle of the main keep rather than on the edge. This is not unusual, and was a design feature present in some Germanic castles. Take, for example: Wartburg Castle:
Much like the Siege castle, we can see that the Donjon rises out of the central keep, which itself is rising out of one of the big buildings. Granted, it's not perfectly centered, but close enough for these purposes.
Beyond that, we can see that the castle uses a mansard-style roof:
This is truly unusual, as mansard roofs typically weren't used on castles until much later on when they started evolving into palaces, mostly because mansard roofs are a visual extravagance, and don't really offer defensive measures. The Siege castle is not a palace, however, as it's too well fortified outside of this, which is especially apparent given that it has stone where the roof flattens out, as well as on the upper areas. This is a strong defensive feature, as it's not as flammable as wood while being a lot tougher, but at the cost of being more difficult to build. In fact, this tells us that the castle features a vaulted ceiling:
Of course, a castle with all vaulted ceilings is also not unheard of. Don't believe me? Look no further than Dover Castle:
The central keep has a complete stone roof, only possible via vaulted ceilings. So, absolutely possible. That being said, I've never seen a mansard roof combined with a vaulted ceiling, but it's possible. Likely impractical, but possible.
Moving on, there's a small courtyard on the upper level, complete with a central statue. Nothing informative (apart from the further evidence of a vaulted ceiling), I just thought it looked neat and wanted to point it out.
Now here we see the main entrance to the keep. This, by the way, is why I kept referring to the castle as having an entirely vaulted ceiling; this door implies that there is an entire level on the ground. There were castles which did not have a level on the ground, and the interior instead sat on an elevated stone foundation, but they were in the relative minority.
Now let's take a closer look at the bastions themselves. The very presence of the cannon platforms shows that this castle likely wouldn't have been built prior to the 13th century, as that's when gunpowder (and especially cannons) rose to prominence in Europe. Interestingly, the cannon is situated upon a vaulted(ish) platform. Bastions of this type were either hollow with staircases or solid:
As you can see, the amount of cannons is different. Though, to be fair, the cannons featured on Siege are absolutely enormous, rivaling even the Tsar Cannon in size:
Yeah, this castle has some serious firepower.
Moving on, let's look at the main gate. This is... interesting to say the least. It appears to have once held two large wooden doors (which are now missing, likely removed for various reasons after centuries of disuse). However, there doesn't appear to be any sign of a portcullis, nor anything resembling a traditional gatehouse:
This means that either resources were low when the gate was constructed, or that the castle was built later than what we think of as the Medieval period. Portcullises and gatehouses were intended to protect against waves of infantry and older siege weapons (such as battering rams). So far, nothing about this castle indicates that it was intended to protect against such threats, and therefore isn't a traditional style of castle. Instead, this is something known as a "Bastion Fort" or "Star Fort":
These rose to prominence in the 1500s as gunpowder became the cornerstone of European warfare. They were designed specifically to deflect cannon fire and provide protection from incoming musket fire, as many siege weapons of the medieval period were rendered obsolete by these advanced weapons.
There are more details I could point out (such as the two rear bastions having random wooden roofs, or the large wooden area behind the keep that serves no discernable purpose), but this analysis covers everything I wanted to talk about. I hope you had as much fun reading this analysis as I did making it.