All my plans shown in this thread fit the size limit for the contest. Use your imagination to modify and customize them!
This could be a stand-alone starter layout and later expanded to the right.
A loco and two ore cars work the steeply graded branch.
A through train on the oval sets out and picks up cars at the spur, and lays over in the tunnel.
This O27 loop-to-loop arrangement is a really tight fit for the micro format.