It has been a staple of many years the suggestion of travelling to or from Lugano (or elsewhere in Ticino region) or Italy and Switzerland via the Gotthard railway and getting a "free" scenic sightseeing without adding to travel time.
That is no longer possible. Since Dec 11th, 2016, scheduled trains travel through the brand new Gotthard Base Tunnel, which is very long 52km tunnel bypassing almost all the scenic mountainous part of the route. The transalpine trips are now also significantly faster (more then 30min time savings).
If you want to travel over the old line, you need to take regional trains stopping at all stations. This is not possible with train-specific tickets but easy with domestic open tickets. However, that takes one extra hour to accomplish compared to previous travel times, in most combinations, and 2 transfers.