This paper introduces an open-source software toolkit for combining the Robot Operating System (ROS) and Unity3D to versatile robotic applications involving virtual environments. Despite the availability of high-quality robot control and simulation systems like ROS, there is still no framework available for designing complex human-robot interaction tasks and making use of Virtual Reality without expert knowledge in robotics and ROS. Virtual Reality, especially involving head-mounted displays as well as various input and feedback devices can increase the experienced sensation, improve the understanding of certain 3D scenes or provide a test environment for the training of non-expert operators. As a solution, we propose Unity3D for designing the interaction interface to virtual and real robots. Our implementation of the bilateral communication layer between Unity3D and the ROSbridge and the importer for XML-based files in Unified Robot Description Format allows synchronizing the state of the real robot and the one of its simulated counterpart in the Unity3D environment in a very comfortable way (see Fig. 1). Using the proposed system we present different use cases and demonstrate how to prototype different interaction concepts efficiently.