A sun tunnel is not so self explanatory, but it is also a nice way to get lots of natural light into your space. Where a roof window is just a straight forward window in the roof; a sun tunnel has an opening that goes in your roof paired with a column of reflective material that traverses the roof space to your ceiling, then an opening in the ceiling as well. They work well with multiple story houses, or if you have a roof space that you generally use as a loft – full of insulation and boxes of old Christmas decorations.