While display quality and rendering for Head-Mounted-Displays (HMDs) has increased in quality and performance, the interaction capabilities with these devices are still very limited or relying on expensive technology. Current experiences offered for mobile HMDs often stick to dome-like looking around, automatic or gaze-triggered movement, or flying techniques. We developed an easy to use walking-in-place technique that does not require additional hardware to enable basic navigation, such as walking, running, or jumping, in virtual environments. Our approach is based on the analysis of data from the inertial unit embedded in mobile HMDs. In a first prototype realized for the Samsung Galaxy Gear VR we detect steps and jumps. A user study shows that users novice to virtual reality easily pick up the method. In comparison to a classic input device, using our walking-in-place technique study participants felt more present in the virtual environment and preferred our method for exploration of the virtual world.