Edinburgh
Quaint, old city. You can hit representatives of all the Scottish highlights within walking distance of each other.
Edinburgh castle has Scottish history and the Crown Jewels.
Walk the "royal mile" - we used Rick Steves, but there are numerous walking tours.
At the other end of the mile is Holyrood Palace - a residence of Queen Elizabeth.
Additionally, there's a steep mountain climb available near the palace with a good view and along the 'walk' there's The Whiskey Experience which teaches about types of whiskey, gives you a taste and an opportunity to buy some.