One of the Ambient Structures from Katters Structures.
There are two kinds of Sky Decor:
Villager manned hot air balloons and blimps.
And Pillager manned battle blimps.
The main blocks are :
In Villager versions you can find maps to most Structures in Katters Structures inside chests
Sky Decor, will naturally spawn over Grassland Bioms and their corresponding Biomes O' Plenty and Terralith Biomes.