High level clouds never look as convincing as lower altitude cumulo types.
On a group flight the other day I was particularly impressed by what I saw:
Until I looked straight up:
That looks straight out of Minecraft.
There were less blocky, right angled cloud elsewhere, but other than the obvious something else struck me. The clouds appear to be inverted. They are completely transparent in the centre of their structure, and they get thicker at their edges.