Don, here are some pictures of my clockwork layout in its current form... I'm afraid it isn't very photogenic, lots of background clutter!
First, this is the north loop where the enginehouse, water tank, and coaling tower are located, as well as the north yard:

Heading out of the north loop, the tracks come together for a short section of double-track mainline. It's also where one of the crossovers between the mainline tracks is located. Since it is a central location of the layout, it also happens to be where I keep keys for winding up the locos... you can see some of them at the edge of the layout:

The double-track mainline splits again at the right side of this picture to go around the south loop. There is a small yard area within the south loop, and most of the industries are located inside the loop. The trackage also includes the other crossover between the mainline tracks:

Another view of some of the industries inside the south loop:

Finally, an overall view of the south loop/yard/industries. It's a little different than the view I posted earlier - I've made a few changes and this is the most recent arrangement:

I tried to use as many vintage metal/litho buildings and accessories as possible for the layout. Since the tracks are 2-rail tinplate, there isn't any power to them - trains are mostly clockwork, although I have a few on-board battery locos that occasionally run on the railroad. As stated above, the mainline is mostly O42 & O54 Lionel (O27 profile rail) with the middle rail removed, and all other track is either vintage Marx or Lionel 2-rail tinplate. The layout uses both Marx and Lionel 2-rail switches. The roadbed is 1/2" MDF cut to shape, painted with gray primer, then painted with stone textured spray paint. The "grass" is indoor/outdoor rug from Lowes - used to be Ecorug, now they changed brands but it is very similar.
This is a trackplan of the layout, although it doesn't show a few of the extra tracks that are in the yard area... I put straight pieces of track down between the yard tracks for extra display area. You can see that the crossovers allow the train direction to be reversed... it allows for some interesting "operation" with multiple trains:

And that's it. I don't get a lot of time to work with the trains nowadays, but still enjoy them. Hope to devote more time to the hobby once I retire!