Castles was a game where you basically just build a castle. But it was more elaborate than it initially sounds. The game focuses on the time it takes to build the castle from the foundation up. The game is finished once it's built, though it repeats itself a couple times as you build a castle in a few different kingdoms before the game is finally over.
In order to be a proper castle, it has to be of a minimum size, so you can't just build one wall and say it's done. But the size of the castle determines the size of your army, and you need to manage resources, labour, and, of course, money, in order to complete it. You need to hire a work force, pay them, tax them, assign how many workers will work on each segment, and what you would like in order to defend the castle. Every now and then, the castle is attacked and you need to fight them off before they destroy your castle. Sometimes they'll manage to knock down a wall or two before you finally run them off.
But my favourite part of the game was that while the castle is being built, you still need to manage your kingdom, and messengers will visit you every now and then and present a situation, and you have your choice of how you'd like to deal with it. Some storylines go on for a few visits, and the choices you make will affect things like your popularity and morale.
It was a great game; I don't know how well it runs on newer systems, but it's worth tracking down for some old-school fun.