The National Gallery of Scotland sits at the foot of the Mound, the artificial hill connecting the Old and New Towns, and it is one of the finest small national galleries in Europe. The collection covers European art from the early Renaissance to the Impressionists, with particular strengths in Italian and Dutch masters, 17th-century European painting, and Scottish art from the 18th century onward.
Entry to the permanent collection is free, which makes it easy to drop in for an hour without guilt. The suite of rooms is manageable — unlike the vast galleries of London or Paris, you can see the highlights in a focused two-hour visit without exhaustion. The adjoining Royal Scottish Academy building hosts major temporary exhibitions (ticketed). The galleries open onto Princes Street Gardens, which makes a combined visit very easy.