Using multiple environment assets in a single level.

I feel like an idiot because I can't seem to find a guide on how to do this and I feel like there has to be a way.

I want to multiple environment assets and put them in one larger world. So like taking this village https://www.fab.com/listings/69e1b46a-c035-4a4a-b270-099534cedfc0 and then have this castle https://www.fab.com/listings/2906dfe8-b17c-4ef6-8765-94b39a676993 just beyond the village.

The assembled environment assets come as a map and I can't figure out how to drop the map into a larger world.

Is this possible or do I need to assemble the environments myself in the larger world?