From the World Heritage inscription:
The people of the Netherlands established a trading settlement at a fine natural harbour on the Caribbean island of Curaçao in 1634. The town developed continuously over the following centuries. The modern town consists of several distinct historic districts whose architecture reflects not only European urban-planning concepts but also styles from the Netherlands and from the Spanish and Portuguese colonial towns with which Willemstad engaged in trade.
Curacao is unique among the former Dutch colonies in the Caribbean. It has a very European flavor compared to nearby islands such as Aruba and Bonaire. Even today you will see more European tourists on Curacao and you will be more likely to find Dutch actively spoken than on the nearby islands.
View my complete list of UNESCO World Heritage Sites