Will be going early September so are there any other surrounding areas or towns that you might suggest visiting?
I assume that you will plan on seeing Bolzano's Ice Man museum on the way in or out.
George,
Hiking is one of the most popular activities in that area, and Alpi di Siusi offers numerous possibilities, with many of hiking trails accessible by cable car or chair lift. Depending on what mode of transportation you're using, you could visit nearby towns like Castelrotto or Ortisei.
Can you elaborate on "near" and also on what you like to do? You have one full day and if the weather is good, the Alpe di Siusi itself is worth that day if you hike. If you are not hikers, you can spend an entire day in Ortisei riding lifts to the various viewpoints: Mont Seuc, Rasciesa, and Seceda.
There are lots of castles nearby if those interest you.