Venice to Lucerne, Want A Scenic Train Ride

I have avoid answering this question in the past because I am slightly negative on taking trains for the scenery. Must be a slow day. I don't think of any of the rail lines are being particularly scenic. Railway right-of-way areas tend be over grown with trees and shrubs, telephone poles, high banks, etc., that tend to hinder the view regardless of where it is. Often times for few minutes you can catch sight of fields, mountains, etc., but for the most part if is just a lot of clutter flying by the window especially on the high speed trains. So, I would simply chose a route for convenience and schedule. There are some high mountain trains in Switzerland that are designed to be scenic but the routine intercity trains are not. A few years ago we took the train from Milan to Lucerne and there were patches that were nice but for the most part fairly bland.

There are several scenic routes that will get you to Luzern, but you pretty much have to get to Milan to start. That part is easy, there is a fast train from Venice to Milan every hour.

Now descision time. The most scenic route (IMO) is the Bernina Express. Train to Tirano along Lake Como, then the Bernina Express to Chur, then train to Zurich, then train to Luzern.

Another route is the Gothard Panorama Express. Train to Lugano, then the GPE to Fluelen, then transfer to a lake boat to Luzern.

Lastly, take a train to Brig, then train to Spiez, then train to Interlaken, then the Interlaken-Luzern Express over the Brunig Pass. Give yourself extra credit by taking the "Loetschberger" train between Brig and Spiez.

The SBB site is the best site to use for trains (and other transport) in Switzerland. It is, like all rail sites, designed to get you from A to B in the shortest time. It doesn't have any route ranking for scenery.

This website gives some information on the most scenic rail routes through Switzerland: https://grandtraintour.myswitzerland.com/en/
There are other scenic lines, and most of the ones listed are going in the wrong direction for you in this case.

Here is a rail map of Switzerland: https://www.sbb.ch/content/dam/sbb/de/infotexte/uebersichtskarte-sts.pdf
I suggest you look at this while reading the below, or print it out and mark highlighter pen.

The route from Venice is : Venice - Milan - Luzern. There are 3 routes into Switzerland from the south, all via Milan. Milan is off the bottom of the map.
The quickest route, the one SBB will give by default is: Milan - Chiasso - Lugano - Bellinzona - Gotthard Base Tunnel - Arth Goldau - Luzern. The Gotthard Base Tunnel is the long dashed (- - - -) section you can see on the map. You will be "inside" the Alps, going fast but see nothing. You will see bits of the Alps before and after the tunnel.

Option 2 is using the old shorter Gotthard Tunnel. The route: Milan - Chiasso - Lugano - Bellinzona - Airolo - old Gotthard tunnel - Göschenen - Arth Goldau - Luzern. Notice the spirals on the rail line before and after the tunnel. The rail line does go round in circles to gain or loose height. You see more mountains this way, but it takes longer.

Option 3 is "going over the top". Tgis takes much longer and probably cannot be done from Venice in one day, it needs an overnight stop somewhere: Milan - along the east side of Lake Como -Tirano - over the Bernina Pass - St Moritz - Chur - and then round the north side of the Alps to Luzern.
Google for videos or pictures of the "Bernina line".

You can force the SBB website to choose whatever route you want by adding "via" locations to your search.

Thank you very much for all of this information. I really appreciate it, including the comments about the train rights of way!

I highly recommend the Bernina Pass route if you have the time. It does not have to be the named Bernina Express with special cars; regular regional trains use the same tracks hourly. You will need to spend the night somewhere on the way to break up the journey. When we did this we spent the night in Varenna (on Lake Como) and also in Samedan in Switzerland.

All other routes will use tunnels under the Alps to some degree. The old Gotthard Pass route outlined by Chris has shorter tunnels, not the long Basistunnel, so would be my second choice. Again, you do not have to ride the named Gotthard Panorama Express to take this route; you just need to know the stops to choose the regional train instead of the faster intercity train that uses the long and deep Basistunnel.