The European Spallation Source Neutrino Super Beam (ESSnuSB) project aims at a discovery of leptonic CP violation with a precise measurement of the CP phase angle. ESSnuSB is characterized by an intense neutrino beam to be produced at ESS by a 5-MW proton beam, and the placement of the far detector at the second oscillation maximum. The aims of the near detector for ESSnuSB are neutrino flux and interaction cross section measurements. For this purpose, designs consisting of a fine-grained tracker and a 1-kiloton water Cherenkov detector are under investigation. On the other hand, the far detector will be a water Cherenkov detector with an estimated fiducial volume of 500 kilotons. The design considerations include an evaluation of the stability of the detector hall and excavation sites in deep underground mines. All of the detector simulations are based on frameworks which involve Geant4. A versatile event display toolkit for visualization and physics outreach activities has been developed.