This paper describes the "Sickle Cell Counselor" (SCC), a goal based scenario on permanent display at the Museum of Science and Industry in Chicago. SCC is an exploratory hypermedia simulation program which provides users with a basic understanding of Sickle Cell Anemia. The user of the program plays the role of a genetic counselor, and, while playing this role, can do laboratory tests, calculate risks, ask experts for information, and advise clients about the results. The paper begins with a brief description of the SCC which emphasizes the design features most relevant to the patterns of interaction that emerged. These include the design of the task presented to the user, the organization of the database, and guidance given to the user by the system. Three evaluations of SCC which were conducted with museum users in order to better understand how they interacted with the program, are also presented. These studies examined patterns of usage, the cognitive gain of the program, and the effects the counseling task had on learning. Discussions of how particular features of the program affected the interactions of the users and their implications for the design of computer-based learning environments conclude the paper. (Contains 17 references.) (JLB)