Yesterday I found additional informations to reach the castles. From Bellinzona station take bus nr. 4 to Sasso Corbaro (the highest one)
Walking down will take less time than walking up.
Every Saturday there is a market (from 8 am to 1pm )
For people who are in the region:
From 27- 30 September ther is a big cheese market on Piazza del Sole
I did not find informations in English, but on Saturday there will be a big parade from the station to Campo militare
You can find a map here, the green line shows where the parade pass