Blasts from explosions can cause considerable damage to nearby structures, and understanding this damage is paramount in protective design to safeguard the structure and people inside. Numerically modelling the interaction between the blast (fluid) and structures is thus vitally important, especially in scenarios where a structure's reaction is nearly as quick as the blast. Although numerous software codes and algorithms exist (e.g., [1, 2, 3]), numerically modelling fluid-structure interaction (FSI) can often be challenging due to the complexity of initialising and running the simulations and due to the requirements of supercomputers. Given its importance, modelling FSI should not mean sacrificing efficiency, or ease of use, or accuracy. In this presentation, we introduce VIPERFSI, a powerful yet user-friendly solution for fast and accurate FSI simulations. By leveraging VIPER BLAST for fluid dynamics on the GPU and OPENRADIOSS for structural analysis on the CPU, VIPERFSI optimizes the strengths of each platform to utilise the entire computer. This dual approach enables large, fully coupled simulations to run efficiently (even on a personal laptop!) without compromising accuracy or user experience. Here, we will focus on the immersed boundary method implemented in VIPERFSI, discussing its implementation and its strengths and weaknesses compared to other methods. We will then demonstrate the ease of use of VIPERFSI in validation cases, including cases that model blast against structures of steel and concrete. We will compare the results of our coupled simulation to that of an uncoupled simulation, both in terms of results and computational performance. We will then compare our results to experimental and numerical results in the literature to demonstrate the efficiency and accuracy of VIPERFSI.