The cache is in one of the poles of the stadium fence. You have
a few options. Obviously, you can try to check each and every one
of them (that's what stadium nightmare stands for) or, you can play
a game.
The fence consists of 192 poles and four gates. WHEN COUNTING
POLES DO NOT COUNT THE ONES THAT HOLD THE GATES. There is a series
of poles that lead you to the pole where the cache is hidden. At
the given coordinates you will find a pole number one. It will be
marked with a yellow-green duct tape. Pole numbers increment
clockwise and keep adding up as you do full round around the
stadium. The first lucky pole is pole number 4. Inside this pole
you will find the number of the next lucky pole. Inside that you
will find the number of the next one and so on. You can follow the
lucky poles till you reach the pole with a cache and experience
stadium nightmare by walking around it several times OR you can
crack the code. Lucky pole numbers are not random, each number is
made from a previous one by applying simple arithmetic actions to
it. Cache is hidden in 7th lucky pole. If you find out
what actions you need to do to get next lucky pole number, you can
count what will be the number of 7th lucky pole. By the
way, you don't need to enter the stadium, you will just cause an
unnecesery attention this way, everything you need you will be able
to reach from outside of the stadium.