Please suggest which is the cheapest mode of travel from Rome, Italy to Interlaken, Switzerland. What is the best month to go there? What are the best places to visit if one books hotel in Interlaken for three days? How much does the ticket/pass cost to visit these places? Which is the best train pass for three days? Can one get the ticket/pass beforehand in Rome before starting the journey? How is the nightlife in Interlaken? etc. etc.

You are asking a lot of questions that people are going to suggest you do a little research on before you start asking all these questions.

My biggest suggestion is to NOT stay in Interlaken. You will not be in the Alps and will be a good 45 minutes away from getting up into the mountains. Better places to stay are Lauterbrunnen, centrally located down in the valley or Wengen, Murren, Grindlewald or Gimmelwald. These are up IN the mountains which is certainly my preference. Grindlewald is the largest with Wengen next, then Murren and then the small village of Gimmelwald which I LOVED but it may not be your cup of tea.

I found that point to point for rail in Europe was cheaper than a pass but once I got to Switzerland the Swiss Pass was a better or deal or at least about the same price as point to point tickets but a LOT less trouble and time consuming. In Switzerland, you will be doing tons of getting on/off all kinds of transportation. The Swiss are great at timing all of these so that when you get off of one you get right on the other. You won't want to have to run to the ticket window or machine in between. I didn't have the Swiss Pass for one of my days and it was such a pain. The Swiss Pass will let you ride anything free, including the lake boats except the highest points in the BO. If it doesn't go to a village where people live, you will have to pay. Last year we had to pay half. I understand you have to pay more this year but I haven't double checked that. You can get a Swiss Pass before ever leaving home. You need to have it validated at the train station in Rome or at least the last train station in Italy where you have a little time between trains.

I'm not sure if it is the cheapest, but most people would go by train.

You should at least investigate the cost of flying.

I agree the swiss rail pass is a help, and that staying outside of Interlaken is better.

>You should at least investigate the cost of flying

Flying would make sense if you get a cheap flight to Bern (very small airport with few flights). Otherwise, whatever you save by flying to Zürich or Geneva will be eaten up by the trip from tehre to Inetrlaken.