As you get off of the bus, stand facinf the main building, and turn right, walk out of the terminus and turn left, walk down the road a little way and then when you get onto the main high street turn right, walk down this until you get to where the road turns a corner and goes up the hill, where it does this walk down the bus only road (the castle will be up the hill on your right) walk down/around this road (its curved) keeping the castle on your right, you will come to a big cross roads, walk over this heading down the hill, keep walking down this road untill you go over the bridge, from there you will see the train station just over the road (big building with a car park out the front with taxi's in it.
Or you could catch the number 25 bus from the main bus station which goes to the rail station, its up to you.
Hope this helps, if not, then PM me and i will send you my number, and when you get to the city call me.
Hex