In this paper we describe the architecture of virtual clot (vCLOT), a virtual world system designed to teach procedural knowledge of blood clotting process, in a game based learning environment. vCLOT utilizes virtual world to give learners an immersive learning experience while actively participating in tasks that require them to apply the procedural knowledge they have learned. Design of vCLOT combines the immersivity of virtual worlds with the power of knowledge structures. Immersivity provides learners with the opportunity to make decisions at every level of the game. This transfers control of interaction to the learner, enabling the learner to be actively engaged in knowledge construction process. Knowledge structures are a neat way to represent domain and learner data. The user interface of vCLOT is designed and implemented with Open Wonderland which is an open-source 3D toolkit. The learning goal which is to learn about blood clotting process, is aligned with the game goal, which is application of blood clot process steps to heal an injury. The game goal is presented as a quest in which the learner interacts with concepts by either dragging them or synthesizing them from other concepts. Learners complete the quest on successful formation of blood clot which in turn implies that they have learnt the blood clot process. We plan to do a usability study to improve the system before starting actual intervention.