LNG terminals are built to handle tankers of specific size, with cargo capacities within a narrow scope. This is related to the differences in cargo, fender and mooring systems used for LNG tanker handling of various sizes. The research problem solved in the article is the development of the method for optimal design of a universal LNG cargo handling facility that enables safe operations of LNG tankers in a wide range of cargo capacity that covers almost entire spectrum of global fleet tanker sizes. The article presents a methodology of optimizing the parameters of LNG cargo terminals to accommodate both small bunker ships with cargo capacity of 500 m3 (50 metres in length) to Q-flex type tankers capable of carrying up to 220 000 m3 (320 m in length). The authors have determined conditions for the safe operation of these tankers in sea LNG terminals and described differences in the construction of cargo, fendering and mooring systems. The optimization of both location and terminal parameters for a wide range of gas tanker sizes as well as approach channels leading to the LNG berths was performed using a specially designed two-stage simulation method of optimization. In the first stage the best location of a universal LNG terminal and its berths in the existing port basin is determined. The second stage defines optimal parameters of approach waterways to the berths of a universal LNG terminal. The optimization criterion at both stages was the minimization of the costs to build and to operate a universal LNG terminal. The developed optimization methodology was actually used in the design of the universal LNG terminal in the outer port of Świnoujście. The tests made use of real time simulation (RTS) and non-autonomous models of ships, in which ship movement is controlled by a human (pilot, captain). Simulation tests were performed on a multi-bridge ship handling Polaris simulator with a 3D projection, from Kongsberg Maritime AS. This full-mission bridge simulator (FMBS) is located at the Marine Traffic Engineering Centre, Maritime University of Szczecin. Two simulation ship movement models were built and verified for testing the manoeuvres of port entry and berthing. These are: Q-flex type tanker (length: 320 m) and an LNG bunker ship, 6,000 m3 capacity, 104 m in length. The test results were used in the design of the universal LNG terminal in the outer port of Świnoujście and approach waterways leading to the berths (now this investment project is in progress).