Ok.. I am going to tell all
First some back ground
There were several of these at one time though the one at Bad Durkheim is probably the biggest.. I suppose the the closest analogy today would be wellness parks..
Basically the gradierwerk runs water down a very large surface, made much larger by ( surface area wise ) what it is made of, brush wood
Saline water from a spring is pumped up to the top and allowed to flow down either side. This releases a mld ozone in to the atmosphere..
There are rooms at the bottom that used to be open and you could sit in to take the cure ( so to speak )
It was getting very tatty and then there was a fire but when the main roads became very busy the local powers that be decided it should be brought back to spec thereby increasing the goodness of the air in the town with the breeze blowing off the miles of vineyards, past the gradierwerks and into the town
It is about 300 metres long and for €1.50 ( might have gone up by now ) you can take the grand tour and walk around the top veranda
So you see many many answers danced around the right one but no one apart from
Oldandbald got it spot on
If you are ever anywhere near Bad Durkheim I would urge you to make the time to visit..Most of the town is really a sight see'ers paradise with a good deal to see... with stuff dating from about 100 AD to modern day ( and yes, for the philistines out there there is a Maccy D's and a Ranch steak house LOL !!!