How to watch photo sphere taken on another device offline on android? Short

I have taken several photo spheres on my old Nexus 5. 

Now I have migrated to the new Nexus 5x, how can I watch the photo spheres offline?

Detail

Since the mobile internet is really limited (something like 2 gigs per month if you're lucky, my private account has 500 megs) I don't want to use a large part of this contingent just for viewing one single sphere. And W-Lan isn't always available. 

Furthermore: The downloading time is really annoying, it takes so long even with a fast (100 mbit) internet connection via wlan - I'd like to zap through the spheres just like I did on my old Nexus 5.

I only use google's own "Photos" App and google's cardboard app for viewing a photo sphere. 
They don't seem to chache anything, as soon as I switch off wlan and mobile data spheres that I have just opened a moment ago using wlan are not available. 

I found no matching entry in the preferences of the "Photos" App and the "Help and Support" pages are just as helpful. This is getting really frustrating and I'm starting to wonder how stupid an app can be :-(

There is an option to "Download" the spheres but all that this would give me is a plane image.

My Motivation

Actually I'd like to show my family these spheres using the pretty decent card board vr :)
In answering my own question, got the answer on https://productforums.google.com/forum/#!topic/photos/SbXGsiE7HLE 
Pasting it here anyway so anyone else stumbling over this post gets it as well :-)

Downloaded Photo Spheres will be opened by the card board app as spheres rather than plane images.