It took me half a day in one direction from St Anton, but dont forget you have to get back. So actually 1 day but the slopes were very bad that day so it took longer than usually
Now seen so many ski regions claiming they have the "longest ski circuit in the alps", some say its the Kitzskiwelt tour, some say its The Challenge at Saalbach-Hinterglemm and some say its the SeiserAlm-Marmolata-Sellaronda
