Preliminary notes:
1-My head includes:
cesium.com/downloads/cesiumjs/releases/1.91/Build/Cesium/Cesium.js
cesium.com/downloads/cesiumjs/releases/1.91/Build/Cesium/Widgets/widgets.css
2-I have only a few landscapes, so I upload the gpx file direct from my site.
I am not good in creating CESIUM scripts, so I asked an artificial intelligence (AI) site to solve my problem, but the AI site was not succesfull.
My problem and my request is: how must I place two gpx files into a script?
In my case: away as gpx-1 and back as gpx-2.
Thx in advance for your hints,
Josef