On the AMS shower front... If you go upstairs near the big communication center (in the int'l part of the terminal) and follow the signs on that level toward the KL lounge that's nearest the F/G gates, you'll pass by a public restroom in the corridor--near the BA lounge IIRC. There are showers inside those restrooms. No amenities are provided (you need your own towel, etc.), but they are free to all, very clean, and usually deserted.