interlaken to venice

Interlaken Ost > Luzern via Brunig Pass (some of the trains are sold as Golden Pass - the cars are slightly nicer in First, but I prefer the old normal cars with the opening windows so I can get lungs full of fresh mountain air not air conditioning, they all take the same amount of time and stop at the same places). The train starts out along the shores of Lake Brienz all the way to Brienz. The train changes ends at Meiringen which is a matter of feet from the Sherlock Holmes Museum with the bronze statue of the great detective nearby, and a few hundred metres from the Reichenbach Falls where he and Moriarty fought to the death. You can take a funicular up the falls. From Meiringen the train climbs sharply up on the rack over the Brunig pass with all its very tall trees and views of the waterfalls. Change trains in Luzern to the main line trains. Luzern > Milano. The train winds up and around the mountains to clear the Gotthard Pass and does sevewral dogbones and loops in the mountains so that you pass and see the same church from several different angles and both sides of the train. You then pass by lakes after Lugano on the way into Milano. Change trains in Milano. Milano Centrale > Venezia Santa Lucia. The Frecciabianca train on that line is quite fast, but not the fastest Italy offers because the track is not the smoothest, and goes through Verona, Vicenza, Padova and goes over the causeway over the edge of the lagoon right into Venice. The ride from Milano as far a Venezia is fairly flat and uninteresting but if you sit on the left side facing forwards you may see the Alps off in the distance to the left. It is quite a long journey.

The route that Nigel recommends is indeed very scenic, but might be tough to do in a day. Check sbb.ch for schedules. Another good scenic route is via Speiz, Lotschberg, Brig, Simplon, Milan. You'll go along Swiss as well as Italian lakes. If you go that route, make sure your train uses the old line over the Lötschberg rather than the new tunnel (look for via Lötschberg-Bergstrecke when searching for your train or ask at any station). The north ramp is very scenic and once you pop out of the old Lötschberg tunnel on the south side of the alps you skirt the mountain very high above the valley below. Incredibly scenic. Another option if you have two days (and this is the most scenic) is via Brig, Andermatt, (Furka/Oberalp passes) , Samedan, (Albula/Bernina passes) Tirano, Milano.

Thanks for the useful information.