One of the most prominent features of the early 80's LEGO castle sets was their modularity. You could attach different models together to make a bigger castle. Really taking the LEGO concept a step further when you can build your own creations out of the sets themselves, not just from the bricks they consist of.
I have all the buildings from those early sets in my collection. Some sets even twice. So I'm able ro make some quite big castles out of them. Many of the sets aren't even meant to stand on their own as they are basically just individual buildings or sections of wall representing some functions of a castle.
Unfortunately for some reason LEGO stopped utilizing this mechanism and instead started producing self sustained sets with no way to connect them together. The last castle theme - the Dragon knights only had two buildings that could (in theory) be attached together. They however don't do so conveniently, producing a bit awkward setup between the two sets.
Luckily these sets are quite popular and there is an active community producing solutions to these kind of problems in the form of MOCs (My Own Creation) with clear instructions how to build them. Of course I could have build my own as well. Searching for a solution to connect those two sets together I found a really nice looking creation that adds two corner sections with towers in between the sets, creating a more satisfying end results. I was also happy to find out I already own almost all the pieces to build this extension!