Tunnels and a bridge will add interest to a layout. You’ll need a rail station too. Put operating signals at crossings. Use either a set of crossing flashers or a flasher and drop-arm combo. Kids (and adults too) are mesmerized by these ‘lights and action’ items.

Other ideas like a working grain elevator, water tower, coal loaders, or a control towers help complete a scene. Be creative, but specific, with your scenery.