Sanjeev- Don't know if you have Elite status with NW, in which case you could possibly get a pass on your own, or if you are on the US$500. BC fare I'd posted, but isn't the flight you are on a KLM/NW code share? As a BC pax, you could gain admission to the 2nd floor NW/KLM Business Class Lounge next to the KLM Royal Wing Lounge (for Flying Dutchman members of any stature) by showing your ticket. I actually don't recall any showers here, just a hotel situated at each end, east and west- but they do seem to have everything at Schiphol, so it would not surprise me.

Recall also that a US Amex Plat card will also do the trick here!