Darmstadt is a lovely area in Germany.  Though the city has a population of approximately 140,000 people, there are still numerous trails and patches of woods to keep the area from looking too urbanized.  Just behind one of the kasernes of the American Army base, is a rather intersting patch of said woods.  It looks as though many of the paths were once roads that have been reclaimed.  Although there is no obvious trace of asphalt, there are manholes right in the middle of the paths.  Very unusual for the middle of the woods.  Also, many of the paths have road names that come up on most mapping programs.  As you walk along, you notice a number of pieces of "art."  At least that's how I can best explain them.  There are items like the one pictured above, that are just too odd to be natural.  This letterbox is hidden by one of these pieces of "art."  I can assure you it is not the one pictured above, as that would give it all away too quickly.  Solve the virtual clues and you will see the "art" it is near.

As for the clues, these are a little more tricky than other ones I will post, as most people aren't familiar with Darmstadt.  However, the answers can easily be found on the Internet.  Do a search of Darmstadt on Yahoo and don't get discouraged.  Just because the city's main page is in German, does not mean all pages are.  Poke around and you'll find the answers.

The secret word is 13 slots or letters long.

FINAL HINT: The secret word is what the carved stamp depicts, not a jumble of letters.