I'm currently working on a project with a windowless bathroom and came across this great way of faking it - a back-lit shoji screen.  Such a cool idea by Mark Brand Architecture.  Then I noticed the stone cladding on the wall and bath panel.  I've been seeing this idea quite a bit recently, including when design hero Abigail Ahern recently clad the interior walls of her garden cabin with dark grey slate (top right picture).  I love that it brings the outside inside and gives the room immediate texture and cosiness.  

get the look

These are the Hartington Tiles, £149 per m2 from Fired Earth.