......you can expect the railway station ticket office to be closed. And you may find, as I did, that the ticket machine isn't working either.
To avoid problems you could, of course, buy a return ticket from wherever you started. But this wouldn't work for me, as I'd intended to stop off elsewhere on my way back.
Fortunately, there were signs at the station telling visitors where they could buy tickets (it's obviously a frequent occurrence). I'd suggest you go to the Bar Beretta (you'll pass it on your way into Varenna) rather than the travel agency (see tip below).
NOTE: I have received information (September 2013) that Bar Beretta no longer sells train tickets. I can neither confirm nor deny this personally.
If you find, as I did, that none of the validation machines are working then you should go straight to the conductor when you get on the train and explain why your ticket is not validated. There are on-the-spot fines for non-validation, and they do check. By finding him/her and explaining you will (in theory) avoid a fine.
With regard to the buying of train tickets and the problem if the station ticket office is closed and the ticket machine dead:
As you walk down into Olivedo (the village adjoining Varenna) you will see the sign in the main photo. Don't be misled: this is *not* the 'last stop' for tickets. You *can buy them next door, at the Bar Beretta.
I went into the travel agency. The girl tried to buy me a ticket but said the site was 'not working'. Her only suggestion was that I 'pass by' later (no mention of the bar next door). Given that the office is closed from 12.30 - 3pm, and that I wanted to move on long before 3pm, I found that idea a little worrying.
So I tried the bar next door (as suggested on the station notice). No problem at all: a nice smiley lady gave me a ticket from a big pile by the till, I paid her, it was sorted.
Knowing that travelling without tickets on Italian trains or buses is not a good idea (especially if one has little Italian) and is potentially *very* expensive in terms of fines, I really could have done without those few minutes of worry caused by the 'site not working' statement .
*NOTE: I have received information (September 2013) that Bar Beretta no longer sells Regionale train tickets and that the station is neither staffed nor has a ticket machine. I can neither confirm nor deny this personally, but it is something worth taking into account if you visit Varenna.
You can buy a return ticket to Varenna from wherever you begin, of course. But otherwise, as soon as you board the train from Varenna, go and find the conductor/guard. He/she will be somewhere in the train and will sell you the ticket. Don't wait for him/her to find you, because doing so greatly increases the chances of you getting a fine for not having a ticket.