If you take the train out of schiphol airport, it's like a 15 minute ride to amsterdam central. Get off the train, walk outside and go across the bridge you'll see infront of you with a million bikes chained to a fence and each other. Walk down the street that is infront of you when you cross the bridge. Take a left on the first road you come to I think, and on your left not too far down that street will be Sensi seed bank. The train runs every 30 minutes, so they whole thing should take you about 2 hours tops, unless you want to hang out. If I'm wrong, you're within a few hundered meters of it. Ask somebody, they'll tell you.
Just speak English. Don't try Dutch unless you're fluent. It will piss them off.
Good luck, tell me how it works out. There are others you can find. That one is just crazy close, and well founded.
