The New York Society of Model Engineers operates both large O-scale (i.e. Lionel size) and HO model railroads side-by-side in a wholly-owned building in Carlstadt, NJ. Here is a scene on the O-gauge pike. A pair of New York Central Fairbanks-Morse C-Liners crosses over a Reading T-1 4-8-4 on the middle level.
One of the beauties of O scale is that the large size allows for plenty of detail both on the trains and the surroundings. You sure need a lot of space, though. It helps to have a building to devote to the effort. Also, note how skillfully the painted backdrop is blended into the 3-D scenery.
Thanks to the society for opening up the railroad to visitors each holiday season.
Model RailroadsFuture TPOTD