I've travelled using Interrail on numerous occasions and am shortly to embark on my first trip since covid. I'd recommend checking out all the links above but read them carefully because what you can use your ticket on varies from country to country. In Germany, for instance, you can use them just about everywhere, but in some countries there are restrictions or there are supplements or booking fees to be paid on some trains. I think Switzerland is OK, but I haven't travelled in Italy so can't comment. I'd also recommend signing up to the Interrail website as they quite often do offers (10% off or first class for the price of second class, for example) which can be quite advantageous.