Time for "Guess that construction"

There is a house being built just down the street from us.  They excavated and then poured the footings, just like you would expect.  Then things took a bit of a turn.  They spent about a week building a pair of large, very involved metal frames.  They looked like they would be some form of wall. Then they attacked them together and stood them on end.

At this point, we were all wondering what in the world this funny metal wall was.  Two days later they came and filled the gap with concrete. 

 As far as I can tell, the elaborate metals walls were nothing other than the forms for a 30 foot high, fairly thick concrete wall.

Now we are left wondering why this wall is so tall, so thick, and so out of place.  I asked one of the workers what it was and he helped me by offering "a wall I think."  The best guesses from the neighbors are:

• Waterfall
• Climbing wall
• Support for some serious roof beams

Any other ideas?