I added a deep and cold mountain lake in the middle of the layout and let it drain to the side under the mainline. The base was a piece of plywood that I painted varying darknesses of grey and black. The middle is darkest to represent the deepest water. I then added different sizes of rock and ballast around the edges. I used Modge Podge painted on with a 1" brush to represent the water. After a couple of coats, I stippled it to make ripples on the surface. Modge Podge is really easy to work with and I think the results were very realistic.
I made my own tunnel portals, and using the Southern Pacific's Donner Pass snowsheds as inspiration, made my own sheds from 1/8" masonite. I painted them concrete and weathered them with grimy black.
Here is a look at some of the rock work I did using Woodland Scenics rock molds and hydrocal. I painted them with cheap artist acrylics diluted with water.
One item I am proud of is the control panel that I built. This layout is DC and required toggle switches to contol the 5 blocks and track switches which were automated using Tortoise switch machines. I simply used MS Paint to create the diagram, text, and logo, and printed it on card stock. I used two pieces of plexiglass to sandwich the diagram, and then drilled the holes to accept the toggle switches. This is an easy way to make any model railroad look more professional.
I painted a piece of styrene and some small brass wire black and planted them on one of the mainline curves to represent a flange greaser. I painted on some oil black using an airbrush to grime up the surrounding rail.