The paper describes the design exploration environment of the CASTLE system. The environment allows the exploration of hardware and software for complex processor designs. The exploration is subdivided into the measurement phase and the analysis phase. The measurement phase uses a retargetable compiler to determine the performance for a large number of different processors and different programs. These fine-grained data form the input of the analysis phase. It transforms the data into abstract representations that are visualized for the designer. The results are integrated into an HTML-based framework.