I plan to sneak in a couple of stations between the Castle and Exoddus, so I won't be specific, but anywhere in the large empty space right of Edd's castle is good. The tracks go over/through the same wall that the castle sits on. If you want, I can be more specific. Otherwise anywhere in that gap, though closer to the castle than the city corner wouldn't hurt.
EDIT: Ok, I'm being specific. Tracks will cross the same wall as Edd's castle, one at z: -30 and the other at z: -28, unless this is a problem. Before that, they're gonna pass through a station in the woods near your villa.
EDIT 3: The supports for the tracks now reach just outside Exoddus so, Rob, you can see where they'll reach the wall. You can adjust the height of them as you wish (just keep them mob-proof

). There are no tracks on them for the reasons explained in EDIT 2 (and no supporting pillars 'cus I put those in after the tracks, so it looks pretty ugly right now). I'll lay the bones of the station in the woods soon.
EDIT 2: Tracks now extend beyond Dark Castle Station to Farmer's Interchange Station which will have a link to the South Line (for which I'm going to have to extend the station Havoc built).
Also, Ma'Spa Depot is running very short on iron for normal rail so, if you have any spare, donations would be much appreciated. If it's not already been done, I might tear up the rails in the Old Nether.