My last layout was built using typical 70s techniques: L-girder structure, "cookie cutter" plywood subroadbed supported on risers from below, and terrain made of paper towels soaked in plaster.  I wanted to try some more modern techniques, so this micro layout is built entirely on Styrofoam.

A stack of Styrofoam                              Checking the clearance

 
A Tight Squeeze                                The big Ravine