The GRAIL (Gait Real-Time Analysis Interactive Lab) enables functional human gait analysis. The GRAIL combines a fully instrumented treadmill with a self-paced option, an integrated motion capture system, 3 video cameras, and an EMG system. Synchronized VR environments, projected on a semi-cylindrical screen, immerse the patient in virtual worlds and natural walking environments. Parameters of the gait analysis can be used to control the treadmill and the VR environment. Our GRAIL is the first and currently only device of this kind in Germany. We use the GRAIL for example for research in quantification of human navigation behavior and desorientation.