At the Arabella Sheraton in Frankfurt, they too charged me for using the sauna. I talked to the MoD, but that could not solve the problem.

The whole discussion occured a bit strange to my naive mind:

(At the pool)
Clerk: "Do you want to use only the pool, or would you like to use the sauna as well?"
Me: "I would like to use the sauna."
Him: "That costs 12 DM."
Me: "It is a benefit of Starwood Preferred Guest Platinum that the health club access is complimentary."
Him: "I don't know about such thing."

(a couple of its-a-benefit and dunno's later a 2nd clerk suggests to ask)

Him: "So you are from Star... ummh Starwood Pref... what was it?"

(after having finalized this useless discussion I continued the issue with the MoD)

Me: "According to the Starwood terms, health club access is complimentary."
Her: "I have never heard of such a benefit."
Me: "Well, but there are the rules, and you can easily control it by internet."
She: "I have never heard of such rules, and for the rest, pool access is free."
Me: "I got the impression that the compliance with the rules seems to be a bit low over here, as there was also no upgrade..."
Her (getting furious): "There are 20 platinums in this hotel each night, and if we would upgrade each of them and give them free sauna acess..."

Well, finally I gave up. She promised to check - my invoice states clear that she didn't. I was charged, and probably I will state a formal complaint. Especially the phrase regarding the "20 platinums" did IMHO not show a very professional attitude.