Rubens’s Son Nicolaas Wearing a Red Felt Cap by Peter Paul Rubens in the Albertina Museum, Vienna. Rubens has never been a personal favorite but this drawing of his son is quite charming. It is located in the Albertina Museum in Vienna Austria. While a very good museum in its own right, it well known for its massive collection of drawings and prints. In the same vicinity as this drawing were ones by Michelangelo, Da Vinci, and Albrecht Dürer, including Dürer’s famous Praying Hands.

https://en.wikipedia.org/wiki/Peter_Paul_Rubens
http://www.albertina.at/en
https://en.wikipedia.org/wiki/Albertina