"The use of challenges to stimulate enquiry and problem based learning is being introduced into a number of real estate courses throughout Europe. At the same time the built environment professions are moving towards a more multi_disciplinary and international approach in solving ever more complex real estate and business problems. There is a need therefore for built environment education to ""collapse boundaries"" between professional disciplines and across European borders and design projects that stimulate, enthuse and capture the imagination of learners. This working paper examines the evolution of a challenge based approach, the associated support required to be effective and proposes a model to calibrate projects, which will be tested in future research. Taking the reader through one of the projects, it critically examines the role of the challenge aspect and provides a critical and comparative evaluation of the project through student and tutor feedback and structured focus groups. The paper: * outlines the pedagogic underpinning of the use of ""challenges"" * describes a series of innovative challenges * evaluates the challenges from both tutor and student perspectives * proposes a new model to calibrate and test the challenge of projects. There is a plethora of articles and papers around problem and enquiry based learning but relatively little in terms of the complexity and challenge needed to stimulate deep learning. Written by an advocate of challenge and a practitioner who has been developing complex international ""challenges"" this paper undertakes a longitudinal review of a project that has run successfully for a number of years. In conclusion it proposes that challenge is an essential component of successful problem/enquiry based learning and the effectiveness of projects relies on a series of inter_connected variables that could be measured to examine future projects. Keywords: Autonomous Learning, Multidisciplinary, Enquiry Based Learning; Role Play, Virtual Learning Environment."