Just guessing but this is on the military training range and there is a supervisor's tower next to it. I think this is used for training the clearing of sewer systems of enemy forces.
Sewer system fighting simulator
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By kjfitz @ 2007-08-17 17:06:11
jbottero
@ 2007-08-18 01:11:03
I am told by one of my Ft Lewis friends that this is exactly what it is..