Don't have room for a physical model train set? OpenTTD is an open source simulation game based upon the popular Microprose game 'Transport Tycoon Deluxe'
OpenTTD is modelled after the original Transport Tycoon game by Chris Sawyer and enhances the game experience dramatically. Many features were inspired by TTDPatch while others are original.
See Play with model trains in OpenTTD
My father has always been fond of model trains, and I remember watching him building a track around the Christmas tree when I was young. When Lego train sets were released, he and I transitioned to them for their convenience and inherent extensibility. We built and operated Lego trains and monorail tracks over the course of many years. I've often imagined a possible future in which I have a garage or a basement dedicated to miniature landscapes and electric whistling trains.