With both hands, Christian Karl parted the imaginary curtain in front of the skeleton made of steel and concrete.
Then it goes up a flight of stairs made of three somewhat wobbly wooden planks to an open area with a raw floor.
"There will be a glass facade here and behind it the bathing hall," says the architect from Friedberg in front of a little more than a dozen guests who want to be guided through the construction site.
The man in jeans and a pea coat points into the room and talks about the reception and the café of the future Sprudelhof thermal baths.
At first glance, it could also be a multi-storey car park.
In this case, however, it would certainly not be the largest construction project in Bad Nauheim in terms of costs.
Karl compares the effort with the construction of the Sprudelhof.
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Between 1905 and 1911, what the city praises as the largest complete Art Nouveau ensemble in Europe was built.
According to the municipality, the construction project cost the equivalent of around 54 million euros at the time.
The new thermal bath alone costs a good 39 million euros.
With a view to the magic triangle of cost, quality and time that is important for his trade, he says things look good everywhere.
Many works were awarded before the recent massive price hike.
Otherwise, it is difficult to negotiate, as he says.
A few unknowns remain on the cost side.
The city is already expecting a surcharge of about a tenth.
According to the architect, it is already clear that the building should be completed in about a year.
It will be bigger than the old thermal bath.
Four elevators in the new Sprudelhof thermal baths
From October next year, visitors will be able to climb the stairs from the underground car park, which is also part of the project and cost almost 14 million euros, to the foyer or use one of the four elevators.
At least that's the schedule.
There is also the idea of being able to promenade from the hotel, which is still to be built, in a bathrobe to the bathing hall.
It takes a lot of imagination to visualize all of this.
For example, how changing rooms are installed above the ventilation ducts.
Or what it will be like under the adventure shower amidst reinforced concrete columns that resemble a crescent on the inside.
On the other hand, it takes far less imagination to imagine a part of the facade.
It consists of slightly curved concrete parts and is reminiscent of the sloping roof parts with skylights in old factories.
The construction is called “Wave Wall”.
This is less architectural poetry than it might seem.
The waveform is immediately apparent, and the allusion to water, the central element of the thermal baths, is obvious.
"Anyone can build right now," jokes Karl.
But there is more behind it than the ambition to show that it can also be curved: the view between the individual concrete parts always falls on the Sprudelhof.
That's the specialty.
On the other side, visitors look over to the Kurpark.
This is not due to the conditions of the shell construction - it will also be the case after commissioning.
That was not possible in the previous building, as Karl explains.
When bushes are trimmed, the view from the bathing hall into the spa park should also be possible in the future, as they say.
But the big trees should remain standing.
Overflow pools will be found in the basement under the bathing hall with the large pool.
They will allow multiple exchanges of water daily.
A few steps away from the large pool there will be one with intensive brine.
The architect leaves it open how high the salt content will be.
But he says: "One will be able to float in it." As in the Dead Sea?
The salt content in the Dead Sea is almost 30 percent, the North Sea has a good tenth.
So it's going to be quite salty in the intensive brine.
Keeping your mouth shut while bathing should then be appropriate.
This is what the experience of bathing in the waters of the Middle East teaches us.
But fans of thermal baths will not only be able to bathe in the new building.
A themed garden is also part of the complex.
Lawn for sunbathing, outdoor pool and showers included.
Don't forget the outdoor sauna.
It will be lower - to discourage prying eyes on nudity, as Karl says.
The sauna garden is the connecting element between the new building and the venerable buildings.
If you let your eyes wander over the new outdoor area, you will inevitably see the Waitz tower with its copper dome.
It was built to pump brine to the graduation works.
That was in the middle of the 18th century.
He looks that old too, blasphemers may remark.
Architect Karl reassured, however: The tower should be made pretty again.
Materials placed in brine
Speaking of brine: Salty water is aggressive, attacks surfaces and even wears out metal over time.
Anyone who has ever looked at an aged facade on the North Sea or the Atlantic knows that.
That's why the construction team placed various materials in brine for many weeks and looked at what became of them.
Result: Some materials have been exchanged for more robust ones.
The architect, with construction manager Alexander Vonderheid at his side, spent almost an hour explaining the current state of affairs and numerous details.
The visitors also accept his offer and ask questions.
For example those according to the energy concept.
Should there be a solar system on the roof?
And for aesthetic reasons.
The new building is to draw energy in three ways: from district heating, brine – and gas.
The architect assures us that this concept was created to the best of our knowledge and belief.
But not only water in the Bad Nauheim underground is in the river.
"The gas component is being reconsidered."