In 12 hours you won't have a lot of time to visit places. The Mercedes Benz Museum is excellent, and you could spend your entire time there if desired. Make sure to go into the basement and sit in the cut away F-1 racer and have your picture taken, if it wasn't cut away on the backside, I doubt that you could enter this "coffin". If you contact the museum ahead of time, you can also arrange to visit one of their motor factories nearby ( www.mercedes-benz.com/classic mention should also be made on this website of the Gottlieb Daimler Memorial, his reconstructed workshop in a park in Bad Cannstatt where the first automobile was created).

Mercedes Benz's largest assembly plant is in nearby Sindelfingen. Visits are best coordinated through their European Delivery Program. Do a google search for mercedes usa european delivery program . But getting there and the tour will use up most of your time.

The current Porsche Museum is much smaller, perhaps two dozen cars that would appeal mostly to racing and Porsche fans. The new museum is scheduled to open sometime in December. Forget a visit to the factory, they've basically quit giving tours with one exception, almost impossible without buying a Porsche through their European Delivery program.

Other things to see:

Many other excellent museums such as the Staatsgallerie for art, Museum am Loewentor for the excellent local fossils, Linden Museum of Ethnology; etc.

The tourist office (in airport or across from the train station on Koenigstrasse) used to give away free maps with a 1-3 hour walk outlined of the sights in central Stuttgart ( www.stuttgart-tourist.de ). I don't know if their 0.50€ map still includes this.

Included on this tour will be the Old Palace with its lovely Renaissance Courtyard, the New Palace, Opera House, Schlossplatz (central square); Stiftskirche (old church); and the Markthalle (market hall) with the sights and smells of gourmet food from around the world.

The world's first modern TV tower completed in 1956, which also has a viewing platform.

Wilhelma ( www.wilhelma.de ) which is Europe's largest combination zoo-botanical garden set amidst the nice Moorish architecture of this former palace. A pleasure to visit at any time of year or in any weather!

The mineral baths. Stuttgart has western Europe's largest mineral waters and three large associated mineral baths. In the Leuze one you can swim in bubbly carbonated water.

Not knowing what else you've done in Germany, you might like to take a quick trip to Esslingen which has a well preserved medieval center, 15 minutes away by S-bahn, and slightly less if you leave from Bad Cannstatt or the stadium stop and the Mercedes Museum.

Do u know where I can buy Cukcoo clocks here in Stuttgart ?

Cheers

Stupid question alert!

Is it safe to swallow the water in the baths/pools? (Not only here, but also in other places like Baden-Baden?) More of curiosity than anything else :p

"Do u know where I can buy Cukcoo clocks here in Stuttgart ?"

The regular Karstadt deparment store (NOT Karstadt Sport closer to the train station) on Koenigstrasse in their clock department on the ground floor sells cuckoo clocks. Even although many may be highly reduced in price, most will be several hundred euros. They're not cheap! I've never really looked for cuckoo clocks, so there might be other places. However, with the Black Forest being so close, you could also visit there for one.

"Is it safe to swallow the water in the baths/pools? (Not only here, but also in other places like Baden-Baden?) More of curiosity than anything else :p"

I think mineral water affects people differently. I'm sure for bacteria there is no problem, but I would try to minimize any intake of water. Between the Berg and Leuze baths in Stuttgart are some mineral water fountains with several distinctly different waters that you can drink out of. My German wife can drink to her heart's content out of any of them, after trying them twice I will never do it again as only a slight taste of it has almost immediate bad effects on me.