Especially the Routes in Switzerland and Austria ;) 

Some more information would be appreciated.  Which countries would you like to visit? 

Do you want to visit the alps or only see them from the train? Do you want to stay over night in the alp region? In that case, are you on a tight budget or not?

If you want a more precise Answer i recommend to share some more details like the ones asked by @AnnaB  :) 

My personal favourite are ofcourse the Routes of Glacier Express (with Regionaltrains) and the Route of the Eurocity EC163/EC164 Transalpin from Zuerich via Sargans - Innsbruck - Bischofshofen - Selzthal to Graz. 
Especially of the Panoramic Carriage on the Eurocity for 1st Class Passengers https://www.vagonweb.cz/razeni/vlak.php?zeme=OeBB&kategorie=EC&cislo=164&nazev=Transalpin&rok=2023

Note that all these many Swiss ´special´ snow-viewing expresses also have normal trains with normal seats without any extra to pay. Swiss are even worse as RyanAir in able to lay on all types of extra to pay. The main site has a complete overveiw.

IMHO the best longer line is from Zürich east via LIchtenstein into Austria-Arlberg line-to Innsbruck.

About the only other country with also Alps is FR-and their raillines do not really connect into Swiss etc.

The route of the Zentralbahn (Luzern-Interlaken) is also quite nice and included in the pass. Panaromic coaches are available without an extra reservation cost.