This is one of a 3-image HDR "story".
The "lead" image, a landscape using a grad ND filter rather than HDR is at - http://www.pbase.com/image/104699558
The same landscape with unnecessary HDR is at - http://www.pbase.com/image/104699564
And finally we have the image you're viewing now which absolutely required HDR if you wanted to show highlight detail (in this case the entire scene *outside* the tunnel) and the shadow detail (everything inside the tunnel). Without HDR you can have one or the other but not both. Of course, some HDR practitioners would have turned this tunnel shot into a cartoon-like image that would fit well into a Batman comic book.
The middle gray areas in the two top corners are the inside tunnel walls (not the outside at the other end). The tunnel is carved through the rock which was left au-natural at the ends and lined with concrete in its interior. I'm standing about 50 feet inside the 610 foot tunnel on a 2 foot wide walk (with tripod extending into the roadway - dumb!) hoping that no cars come along for a while (they didn't).