Jul 12, 2018 - 5:28 PM
Since you'll be coming from Milan the simplest option would be a Swiss Travel Pass (Lucas's 3rd link). You're then covered from the border (Domodossola) to Interlaken too. You would only need a ticket from Milan to Domodossola: www.myswissalps.com/tr aintickets/italy.
Please click to Lucas's first 3 links and go to the "Where it's valid" tab to download the detailed maps of all routes covered by the various passes. The Jungfrau Travel Pass covers a rather small area. It may not be enough to "roam around Interlaken", but it really depends on where you'd like to go. Again, the Swiss Travel Pass is the easiest option. It also includes the trip from Interlaken to wherever you go next (as long as it's within Switzerland).