Software visualizations, such as the software city metaphor, are usually displayed on 2D screens and controlled by means of a mouse and thus often do not take advantage of more natural interaction techniques. Virtual reality (VR) approaches aim to improve the user experience. Emerging new technologies, like the Oculus Rift, dramatically enhance the VR experience at an affordable price. Therefore, new technologies have the potential to provide even higher immersion - and thus benefits - than previous VR approaches. We present a VR approach to explore software visualizations following the software city metaphor by using a head-mounted display and gesture-based interaction. Furthermore, we detail our gesture design and how we implemented this approach into our web-based ExplorViz tool. As first evaluation, we conducted structured interviews where participants had to solve three program comprehension tasks and rate the usability of the used gestures and general VR experience for program comprehension. The participants of our interviews rated the developed gestures for translation, rotation, and selection as highly usable. However, our zooming gesture was less favored. In general, the subjects see potential for virtual reality in program comprehension. This package contains our experimental data.