Lego train sets have always been a great starting point for more creativity! Every train set I own gets improvements, even if just adding lights!
Quite some time ago I did my own 'Polar Express' train - Pere Marquette 1225 in Dark Green and Black to be precise. A great model and runs well on R40 corners and points.
https://rebrickable.com/mocs/MOC-163401/TrainsWithLights/pere-marquette-1225-steam-locomotive-and-coal-tender/#details
Following Lego's release of the 21344 Orient Express, a blend of PM1225 with Orient Express locomotive and tender parts was created! Quite the impressive train set, whether through the eyes of adults or children and a train robust enough to endure a rainy afternoon with the Grandchildren!
https://rebrickable.com/mocs/MOC-165958/TrainsWithLights/pere-marquette-1225-orient-express/#details