The Common Core State Standards for Mathematical Practice (CCSSI 2010) elevate the ways of thinking used to create mathematical results to the same level of importance as the results themselves. These mathematical habits of mind (MHoM), or "specialized ways of approaching mathematical problems and thinking about mathematical concepts that resemble the ways employed by mathematicians," are increasingly the focus of professional development efforts for precollege mathematics teachers. Educators across the country are considering how to implement this approach to thinking about, doing, and teaching mathematics. One way is through an immersive experience in which teachers experience mathematics as learners and rely on colleagues, and themselves, to unpack mathematical ideas. Such experiences provide exposure to an approach to teaching mathematics that embeds and highlights MHoM. The Park City Mathematics Institute (PCMI) provides a high-quality, immersive experience; but as a three-week intensive residential experience, it costs about $3500 per participant, since it includes the cost of housing, tuition, and travel. To help more teachers have access to this experience at a lower cost, we designed a similar program online. In this article the authors list the key aspects of the in-person experience and the design decisions made to preserve the PCMI experience while using the strengths of an online environment. They discuss the changes that occurred as a result of doing this work online and end with takeaways and remaining questions. (A bibliography is included.)