Train from Bolzano to Grindlewald, Switzerland

Just plug it into the Deutsche Bahn calculator:
http://reiseauskunft.bahn.de/bin/query.exe/en?country=USA
Looks like 7 hour and 38 minutes is your fastest, change trains in Verona, Milan, Spiez, and Interlaken.
Look at a date nearby, since there is a schedule change in June, but the changes aren't that big (usually).

The itinerary through Malles and a bus over the Swiss national park to Zernez would be to die for in a good weather day. Probably shorter as distance covered but longer as time needed.

Ann,

I made a similar journey in Sept 2014 and it took nearly 12 hours by public transportation. I did the opposite - train from Murren, Interlaken, Bern, Zurich, Innsburck, Bressanone (Brixen) and finally a bus to Santa Cristina. Beautiful region. Enjoy!

http://www.oebb.at/en/

http://www.trenitalia.com/tcom-en

Bolzano to Innsburck

http://www.oebb.at/en/

http://www.sbb.ch/en/home.html

Innsburck to Zurich. It is probably cheaper to use Austrian rail unless you already have a Swiss pass or half fare card.

Zurich to Bern,
Bern to Interlaken Ost
Interlaken Ost to Grindelwald