Hi,
Not sure yet were in Scotland you are going but if down near the west of the central belt then let me know as I know of a few ruined castles worth visiting like Kilchurn castle near Inveraray (also has its own castle and old jail house), castle Lachlan at strathlachlan which is also next to an excellent place to eat called inver cottage, you can then drive past there to otter ferry, tighnabruaich and then on to a viewpoint over the kyles of bute.
If you are in this area, all these places can be visited in an afternoon but there are numerous other places to see in that area like Arrochar and the Arrochar alps, rest and be thankfull, an early morning drive down loch eck which can be truly spectacular.
Cheers, John