It's very easy to travel from Geneva to Interlaken; just use the Swiss rail website at www.rail.ch to research your train trips.
Some small villages around Interlaken that might interest you are Wengen, Muerren, Grindelwald, & Lauterbrunnen. Villages or towns near Geneva that might interest you are Morges, Nyon, Chexbres, Rivaz, Vevey, & Montreux.
I wouldn't assume that you need a pass. You can enter your itinerary at www.railsaver.com, click on "only if it saves me money," and it'll tell you if you need a pass. Of course, that's only an estimate. You can see all of the passes at www.swisstravelsystem.com.