Well, here's the (Long awaited?) tutorial for how to make a good looking Castle town in RpgMaker 2003. As with all maps, you can make it as big or as small as you like. I personally need the country's largest city to be a respectable size, so I'm going with a 50x50 piece of grass.
Next up comes the walls. These bad boys actually cause a little bit of trouble; you have to be sure that it's not a total box otherwise it looks tacky, but it's pretty difficult to make fancy shapes out of 'em. I decided to add a little entryway for mine, with turrets on either side of the entrance (I didn't use a gate or moat, I don't like having to teleport to the same map, and the moat I tried making looked silly. It's up to you, though). I also changed the back of the castle to the pink nothingness tile and used a parallax background, to make it look like it's at the top of a mountain or something like that.
Now it's time to lay down some housing. House mapping is just about universal with the RTP, so if you checked out my other tutorials, you should have no problem making something that looks nice. Scatter a couple of them (remember to make them asymmetrical!) around the map, as such.
All right! Almost done! Here's where you've gotta add in those ever-so-important pathways. Again, don't make them straight. Even though this is a castle, the same rule stands.
Alright, now that that's done, detail's gotta come in. Keep in mind that this is a castle, not a forest. Trees are fine on the outside, but they should only be placed sparingly on the inside.
There you have it: A castle fit for a king. Of course, mine has no palace, but oh well. If you want to do something like that, add some sort of heavily guarded path, then do your interior however you want. I may or may not make a tutorial for that, I'll see.