Would I really subject a 15 month old baby to a 10 hour rail journey? Probably not. But as I’m not really doing this, let’s enjoy the train trip from Cusco to Puno
or if you want a 3 minute video instead (although it is travelling in the reverse direction)
Would you subject yourself to 10 hours with a baby on a train? Maybe. My own grandchildren were 5 and 6 when we travelled from Avignon to Milan to Naples with one overnight stop. And it would certainly beat 10 hours on a plane.