The journey from Interlaken Ost station up to the Jungfraujoch, the highest rail station in Europe, is an amazing feat of engineering. The last part of the ride up is inside a huge tunnel carved out of the mountains at the turn of the last century. And it runs the entire year - it does not shut down during the winter.

The journey starts at the Interlaken Ost station. There are actually two routes, one via Lauterbrunnen, the other via Grindlewald. It is actually the same train from Interlaken Ost, later the train is split in two. Tickets are good for either route and you can take one route up and the other back to see more of the country. Going via either route you physically change trains twice. Once at either Lauterbrunnen or Grindlewald, and the second time at Kleine Scheidegg, where the two routes come back together. From Kleine Scheidegg you make the last leg to the Jungfraujoch, most of which is underground. The transfers are only a few steps from one train to the other, and they are timed so the wait is short. In the mountain tunnel on the way up the train makes two stops, called Eigerwand and Eismeer, where overlooks have been drilled right out through the side of the mountain. Many people stay on the train since the stops are only about 10 minutes, but the views are very impressive and highly recommended.

If you are traveling using a Swiss Rail Pass it can cover the first leg of the journey (to Grindlewald or Lauterbrunnen) and a discount on the rest. If you use a flexi pass and choose not to make that one of the days it will still get a discount on the journey.

From the top (over 13,000 ft) you can see for miles in all directions. Views are great of the largest glacier in Europe (there are several different overlooks), the ice palace carved out of the glacier, and the overall experience. There are various winter sport activities available also for those so inclined.

Make sure you dress appropriately! It will be much colder at the top, and there might be a strong wind. For example when it is pleasantly in the 70s (F)/ 20s C in Interlaken, it may be around freezing temperature on the mountain. And the outside walking areas are likely to be snow compressed by other visitors, and thus quite slippery in the wrong footwear.

Get started as early as you can in the day as the journey from the Ost station to the top takes around two and a half hours and you want to beat the clouds that have a tendency to roll over the mountains in the afternoon. You will also have less crowding by leaving earlier.

There are several restaurants in the complex at the top, but they are expensive. 

On the way down you can make stops in any of the villages you passed through on the way up ans they are all charming.  Wengen is quite nice.

The trains have windows which slide down and are an absolute boon for photo enthusiasts. The train ride offers breathtaking views via both routes.

For those who are late risers, you can start for jungfrau by taking the 9am train from interlaken ost upto lauterbrunnen from where you change trains to reach kleine scheidegg and from where you can take the final train to jungfrau. for those who are not too keen on doing too many activities at jungfrau - 2/3 hrs is more than good enough and one can head back to kleine scheidegg. here if one wants a change of scenery and wants to see a different side of the mountains then you can take a train to grindelwald instead of lauterbrunnen. and then from grindelwald you can take a train to interlaken ost. so in this way you get to see different views of the mountains while going up to jungfrau and also while coming down