There are certainly plenty of add-on routes out there, some great, some not so great. I haven't allowed myself to be sucked into hours of activity building in quite a while, but my 13-year old son hacks into activity and route building all the time. He's figured out most of it on his own, and a little bit from places like train-sim.com. One of his latest projects was to build the Klamath Northern line to Gilchrist on the Maple Leaf Tracks Oregon Cascades route. I brought him satellite and ground-level photos of the mill complex and its track arrangement, and he went from there.