Wilhelm Tell
Wilhelm Tell Express
The Wilhelm Tell Express runs between Lucerne in the German speaking part of Switzerland and Lugano and Locarno in the Italian speaking part of Switzerland. You can either take the train the whole way or take a boat between Lucerne and Fluelen and then travel by train the rest of the journey.
Lucerne is easy to reach by train from both Berne and Zurich. The Chapel Bridge, built in 1333, is the landmark of Lucerne. You can take a cruise on the Lake Lucerne (Vierwaldstätter See in German) Getting to the cable car station for Mount Pilatus can be little bit painful but if it is a clear day it is certainly worth the hassle.

The famous Chapel Bridge in Lucerne
Note that if you take the boat to Flüelen, rather than train, you add three hours to your journey. The train journey between Lucerne and Lugano or Locarno takes about two and a half hours. If you take the boat, the journey will take at least five hours. But on a nice sunny day, the boat has its advantages. Fortunately, the train station in Flüelen is next to the disembarking point of the boat. Note that the upper deck on the boat is first class. The lower deck is second class.
The train journey goes through the Reuss Valley and then climbs up to Göschenen. The climb up to Göschenen is the most spectacular part of the track. A lot of loops and tunnels have been created to artificially lengthen the track, to make it less steep. In Göschenen you can change trains. If you want to continue with the Glacier Express you need to take a train to Andermatt, it's just a 4 kilometer journey but very steep.
The train uses the Gotthard tunnel (length 15 kilometers) so you are missing out on some spectacular mountain views. Once out of the tunnel, you are in the Italian speaking part of Switzerland. On the way down to Giornico, another couple of loops have been built to artificially lengthen the track.
Depending on your train, you may have to change in Bellinzona, some trains go to Locarno, others to Lugano. The fastest trains make the journey between Bellinzona and Lugano in 20 minutes, and the same for the journey between Bellinzona and Locarno.
If you have time, take the Centovalli Railway from Locarno to Domodossola. In Domodossola, you can either take the beautiful train ride back to Locarno or go down to Lake Maggiore, for example Stresa or Baveno, by normal trains and take a boat cruise back to Locarno. The train between Locarno and Domodossola takes little bit less than two hours. For more information about the Centovalli Railway and cruises on Lake Maggiore, click here

Ferry on Lake Maggiore
Both Locarno and Lugano are popular places in summer, so make sure that you have booked accommodation in advance. The Verzasca Dam is just east of Locarno, it was used in the opening scene of the James Bond movie Goldeneye. You can try bungee jumping like James Bond at the dam. The beautiful scenery around Locarno attracts a lot of hikers and cyclists.
The train station in Lugano is a fair bit above the historical city center. In summer, the bus to Tirano departs from the parking space outside the train station. You can take a funicular, handy if you have luggage and are on your way up to the train station. From Lugano you can continue by train to Milan, the journey takes an hour with the fast trains.

Lake Lugano and Lugano
Personally, I think the Wilhelm Tell Express is only second to the Bernina Express in terms of scenic train journey. Especially if you combine it with the Centovalli Railway. And you can add cruises on Lake Lucerne and Lake Maggiore as bonuses.
For more information about trains in Switzerland, visit the SBB web site by clicking on this link