So I am making a game that uses Cesium ion (bing maps + OSM buildings) and I want players to be able to download portions of the world so that it can load it offline. Can someone help? Thanks!
Currently there is not a straight-forward way to do this, and it is against our TOS. We are currently working on a licensing model that allows for downloads of Cesium Ion tilesets for offline use. The initial version will only allow for downloads of your own tilesets (created from data you uploaded). For example, Cesium World Terrain would not be available for download. Additionally, Bing does not allow for offline use of Bing Maps imagery.
Since you are using OSM buildings however, you might want to consider the option of downloading OSM data directly in something like Blender (I believe Blender has an OSM plugin). You can then import it into Unreal Engine and georeference it with Cesium for Unreal.