Our tour up the Grossglockner was one of the best days I've ever had.
This was helped by our tour guides, we came on holiday with Thomson Lakes and Mountains and the guides they use are brilliant. Our tour took about 8-9 in total, (we came from Zell am See) so its a wonderfully full day.
Going along the High Alpine Road leading up to the mountain was incredible in itself. There's a few cafes and shops along the road so there's opportunity for strudel and a toilet break.
The mountain itself is totally breathtaking, particularly as there's a glacier there too, any photo you see does not do it justice.
If there's one thing you do when visiting Austria, go to the Grossglockner, you will not be disappointed.