I built my 12x12 layout has an operating layout, but I do let them air out every now and then by running around the outer mainline, all 072 curves. Here's the plan of my layout:
There's no fancy trackwork, tunnels, hidden areas, the only features are the swing down bridge at the throat of the Wye to gain access to the room and the Atlas turntable. The layout is flat (or should be, there is a bit of a rise in a couple of areas).
I can run a train around the outer loop whiles switching the 4 industrial spurs on the inner track, and move engines back and forth around the TT and engine house. The track going down the left side by the TT is "Offline" to points unknown (hopefully future expansion!).
