All rail systems serving Stuttgart, the Baden-Württemberg state capital, stop at the main station (Hauptbahnhof) in front of the Arnulf-Klett-Platz (Plaza). This central point is served by all national trains, S-Bahn (Subway) commuter trains, the U-Bahn (Tram system) and busses.  

Stuttgart Hauptbahnhof (main station)
Arnulf-Klett-Platz 70173 Stuttgart[i]
The Hanns-Martin-Schleyer-Halle is about 3 km from the main station.

Bad Cannstatt station
Bahnhofstraße 30 70372 Stuttgart 
The Hallenduo is about 1 km from the Bad Cannstatt station.