You could spend weeks in Edinburgh - months! - and not see it all, so prioritizing for our 1 full day to explore was a challenge. I think we nailed it. We left Ruth (peeking out the window) and Norman's lovely house with Val.
Stone of Scone, no photos allowed), the gorgeous views (and pet cemetery) from the castle, and the beautiful St. Margaret's Chapel, dating to the 12th century, the oldest part of the castle.
£10 (about $14).