Two weeks rail holiday around Europe – what to see and do?

[TimmyWimmyWoo]

I'm thinking of going around Europe with the girlfriend using trains as our primary mode of transport. We're thinking of going for 2 weeks in August, sleeping overnight on trains when we can (in sleeper cars, not couchettes), and staying in hotels elsewhere.

I've done it before just after my A Levels (in 2004), but then I went around Eastern Europe and did it on more of a budget (youth hostels and couchettes).

Has anyone done this recently? Are there any sights that we absolutely shouldn't miss? Countries we're interested in seeing more of are Germany, Italy, possibly bits of Austria, the South of France, maybe over to Croatia. Are there any epic rail journeys we should definitely do? Are there massive additional charges on top of the interrail pass when we use trains in certain countries?

I know this is a very open-ended post, but I'm just hoping to get some tips, pointers and enthusiasm for a bit of an adventure!

So far, we've got Berlin, Rome, Pompeii and Mt Etna on the 'must-see' list – any other suggestions of destinations that are a little out of the way, but still doable by train are a bonus.