A major part of software architecture design is learning how specific architectural designs balance the concerns of stakeholders. We explore the notion of "architectural prototypes", correspondingly architectural prototyping, as a means of using executable prototypes to investigate stakeholders' concerns with respect to a system under development. An architectural prototype is primarily a learning and communication vehicle used to explore and experiment with alternative architectural styles, features, and patterns in order to balance different architectural qualities. The use of architectural prototypes in the development process is discussed, and we argue that such prototypes can play a role throughout the entire process. The use of architectural prototypes are illustrated by three distinct cases of creating software systems. We argue that architectural prototyping can provide key insights that may otherwise be difficult to obtain before a system is built. Furthermore, they define skeleton systems that serve as communication means and knowledge transfer among stakeholders.