One of my primary responsibilities in Avatar has been finding ways of creating kilometer-sized assets that read well from all distances.
I've been in charge of setting up the tech, as well as the visual style.
Here you see some examples of the various floating mountains across the Grasslands. These were some of the first benchmarks for the mountains across Pandora.

Every mountain in the game has been created for the most part in Houdini, where its procedural aspects allowed for frequent iterations at a scalable level.
It also allowed to deal with the large amount of data that come with assets this size, and to create a non-destructive bridge between DCC's and the game engine.