6081: King's Mountain Fortress
The King's Mountain Fortress was released in 1990, and is the first Lego castle to feature a raised baseplate, a dramatic shift from the flat baseplates and regular flat plates that housed previous castles. As a result, this set has significantly fewer pieces than some other castles, especially castles for the Lions faction. Other than 6059: Knight's Stronghold (released in the same year) this is the first set with molded wooden doors, as opposed to earlier sets that only had a drawbridge or makeshift grate to block the entrance.
Like many sets, this one includes towers, a drawbridge, flags, and knights. Two interesting inclusions are that of the maiden and of the ghost minifig, which began appearing in sets around this time. Compared to a lot of castles it is a bit lacking, but it does have a small courtyard which is rare among castle sets.
6086: Black Knight's Castle
The Black Knight's Castle from 1992 also features a raised baseplate, the same baseplate from 6081, but the castle itself is much more impressive. This Dragon Knight castle features the first molded gate piece along with the requisite drawbridge. Take a look at the color scheme compared to past sets. While there is an overwhelming amount of black, there is now a fair amount of grey to offset it, along with a beautiful red roof that really catches the eye. Not only is this castle large, it is also much more aesthetically pleasing than past castles, and is a much more complex build compared to the square castles of the 1980s. Lastly, check out all the horsemen! Very much like the original yellow castle, having so many horsemen.
6090: Royal Knight's Castle
The Royal Knight's Castle, released in 1995, features a new and very large baseplate and is one of the most impressive castles that Lego has ever released. This castle features several very tall towers and some new play features like a catapult. Additionally, it is one of the first (maybe the first??) castles to not have a drawbridge, opting instead to have doors and a grate. This Lions faction set makes me nostalgia hard and is one of my favorites of all time. It also features a king with chrome sword and crown, which will become more popular in the 2000s. Lastly, there is a cloth flag and a cloth cape, two items which became popular in the 1990s.
Next will be the final installment, focusing on the 2000s.