Do a search - this has been discussed countless times.

If you are SkyTeam Elite Plus (which you are if you're NW or CO Plat), you can use any KL lounge in AMS. The lounges are very often crowded. Continental flights arrive on Pier G. Follow the signs to baggage claim and immigration where there will be signs pointing you upstairs towards the lounges. You can use KL or even AF lounges. (Do not go through immigration, of course, to get to the lounge).

CO does not have its own lounge at AMS Schiphol.

Lounge #'s for KL lounges: 25, 41, 52. You can't get to lounge 25 unless you enter the Schengen area of Schiphol, which means you must pass through passport control near Pier C/D. Lounges 41 and 52 are impossibly crowded because of all the plats arriving from the States at the same time and waiting for further connections on KL or NW.

-RM