Horizon Run 5 will be the fifth in a series of large-scale cosmological simulations conducted at the Korea Institute for Advanced Study. For the first time, full hydrodynamics and star formation physics will be included using RAMSES. I will describe the proposed simulation, which will be a zoom simulation with a high resolution region ~70 Mpc/h square and ~1 Gpc/h long, and a spatial resolution of 1 kpc. I will present research conducted by our group to justify the choice of simulation geometry, and the impact of large-scale structures on smaller scale properties in hydrodynamical simulations. I will discuss the effects of the resolution and grid refinements on the outcome of cosmological simulations, as well as the problems still to overcome. Further, I will introduce the other ongoing projects using numerical simulations.