Explore the technical challenges of creating massive, seamless multiplayer game worlds using Unity3D in this conference talk from Unite Europe 2016. Dive into Improbable's collaboration with Bossa Studios on World's Adrift, an MMO featuring a persistent 150x150km game world with full physics. Learn about distributed systems, Entity-Component-System architecture, and how SpatialOS orchestrates thousands of Unity instances in the cloud. Discover strategies for managing hardware resources, player demands, and content creation challenges. Gain insights into fault-tolerant, self-healing systems, automatic persistence, and the integration of custom workers for specialized tasks. Understand how this approach enables multiplayer functionality by default and overcomes both technical and design hurdles in building large-scale simulated worlds.