5 days in Geneva - Chamonix

Hi,

1st week of April - we are travelling to Geneva, plan to visit Chamonix for a day or two. Is it possible to do some scenic train rides from Geneva or Chamonix in France? day trips or even 1 night stay trips?
Are there any old castles (day trips) that we could visit from Chamonix?
Alternatively is it a good idea to travel to Italy?

Thank you in advance