There are some great trips to Loch Lomond, Hadrian's Wall in the Borders south of Edinburgh, Perthshire etc. You can also just hop on a bus from Edinburgh to somewhere as wonderful as Rosslyn chapel - the one featured in the Da Vinci code.
Or maybe you would consider going to Loch Ness over two days instead of squeezing it into one day? Or take a 3 day tour to the Isle of Skye which also visits Loch Ness.
Just saying...