I know someone whose two sons had a model railway which took up all of their bedroom except the bunk beds and the space to let the door open and reach the beds. It ran over a couple of chests of drawers, along a shelf under the window, round the walls, round a curve behind the door, across the room on top of an old table, over a bridging shelf, and joined the top of the chests. all landscaped, on two levels and with no end of detail. To operate it, they ducked under the bridging shelf and stood in the centre, surrounded by trains and track.
When the boys left home, it was all sold off. My friend and husband moved to a different house, with oinly a tiny spare room, but when the husband became housebound, they decided to start again. The same kind of arrangement was set up in the spare room, running from beside the door over chests, round a corner and along under the window, round another corner and along a shelf over the single divan bed, and into a tunnel - a disguised hole into the built-in wardrobe, where it turned and ran along another shelf and out of another hole. This took it to the other side of the room door. At this point a detachable section could be added to join it to cross the door. To run it, you went into the room, closed the door, and attached the missing section. This time it was grandsons (4 of them) who loved it. They could sleep in a room with trains all round them.