Barely two square kilometers, Monaco is the second smallest and the most heavily populated country in the world, a principality famous for wealth, luxury and having had the American movie star Grace Kelly as its princess. It makes a pleasant day trip from Nice with stops at Princess Grace's Botanical Garden, the Monte Carlo casino, the changing of the guard at the Prince's Palace, the Oceanographic Museum and the old town. You can trave by bus, train, taxi or ferry.