How does the largest castle on Earth look like?

Lets start from here:

Many castles would fit among these walls. But this is just a yard before the outermost gate.

When you pass the gate here you are still a long walk from the real entrance:

The tower in the distance is the actual heart of the castle. It's a long walk even if nobody bothers you.

Note that the large windows are most likely XIX century additions when the castle was used as a storage house by the Prussians.

And then when you get inside you reach the castle-within-castle:

Which is protected by a serious gatehouse with all the traps money could buy:

And then there is still another castle-within-castle:

And within this innermost castle there is still the tower to be handled:

So the bottom line is that it was much more practical to create a labyrinth of walls and gates (that can be opened wide for a legal visitor) rather than a very high structure that would require an hour of mountaineering just to get to the bathroom…