In reply to Pietrach:
My immediate thought was Loch Ardinning between Milngavie and Strathblane, but I might be mis-remembering, so check a map or Google Earth first. And I'm not sure if you'd count the Campsies as "mountains".
Edit; scratch that idea, I've just checked and there's way too many trees for what you seem to be after.
Post edited at 12:20