You were told that Mystery Spot 33 is a natural feature located in a national park and given these clues to identify it:

Don't let the door slam you on your ass on your way out.

The long, narrow channels that longships once plied are framed by cliffs that soar on each side.

If you hope to hit a quail on the fly, you'll need steady nerves and a keen eye.

And....  "Upon reaching the end of this engineered incline, you'll typically find a stoplight or stop sign."

The answer is Exit Glacier in Alaska's Kenai Fjords National Park. Located just north of Seward, this much-visited glacier is conveniently accessible by paved road (a key distinction) and a trail leading from the park visitor center.  Exit Glacier acquired its interesting name after the mountaineering party that completed the first-ever (1968) crossing of the immense Harding Icefield exited the icefield by descending this glacier.

Congratulations to Lee Dalton, who was first to supply the correct answer.  Others who submitted correct answers were Eric Nelson, Aron, Anon out west, and RangerLady. All five are eligible for our monthly prize drawing.

Here is how the clues lead you to the answer:

The second clue is particularly useful.  It points to fjords, which can be described as "long narrow channels ... framed by cliffs that soar on each side."  Longships were Vikings vessels closely associated with fjords (being characteristically based in settlements on Norway's fjords).  

Kenai is pronounced "keen eye," a fact that should register when you read  "If you hope to hit a quail on the fly, you'll need steady nerves and a keen eye."

"Don't let the door slam you on your ass on your way out" refers to an exit (presumably a promptly executed one) that should be made with due caution.

The fourth clue, which gave many readers fits, was labeled a bonus and not needed to solve the mystery spot puzzle. Never trust a Quizmeister who has not had his morning coffee.  For the record, clue #4 refers to something that motorists routinely encounter at freeway intersections -- an exit ramp that terminates near an overpass.