Stellaris: Leviathans

Summary pulled directly from Steam - Some text may only be applicable to Steam platform

Space is lovely, dark and deep, but it has secrets it wants to keep. Rich systems defended by fierce creatures, hostile pockets of resistance to your civilization, and the sleeping giants of the universe – the Fallen Empires who may yet be stirred from their centuries long indolence.
In Stellaris: Leviathans Story Pack, the galaxy will be filled anew with adventure and challenge as your new and naïve space-faring empire comes face-to-face and ship-to-ship with a host of dangers and rewards.

Main features:

GUARDIANS

Powerful space entities with mysterious origins and motives. Fight or investigate them to unlock technologies and gain access to great treasures.

ENCLAVES

Independent outposts of traders and artists who are willing to make a deal. Exchange resources, purchase information about the galaxy, or commission a great work of art for your empire.

WAR IN HEAVEN

Where will your fledgling empire lie if two ancient Fallen Empires decide to renew old grievances in a War in Heaven? Will you err on the side of caution and take a side with the stronger power, or will you strike at both whilst they are occupied with their own titanic struggle?