Crystal Dynamics is building production tools tailored to AAA game development for games like Tomb Raider (2013). One of the newest tools is Horizon, an object and world editor. This talk will give an overview of Horizon, and demonstrate its key features including level and object authoring, modular workflow, concurrent authoring, and authoring in context. It will cover the tool's high-level architecture, implementation decisions, and coding gems. Horizon is written in C# using WPF and a C++ back end. The talk will also touch on the pros and cons of work flow, implementation decisions, and outsourcing challenges. Horizon is one of the tools that enable content creators to build the most complex worlds yet to be seen in Crystal Dynamic games.