The Warp Five Complex was a research and development site on Earth, where Henry Archer and Zefram Cochrane, amongst others, worked on the creation of the Warp Five engine.
The facility was located outside Bozeman, Montana. (ENT: "Singularity")
Cochrane dedicated the facility in 2119, making what would come to be an historic speech:
"On this site, a powerful engine will be built... an engine that will someday help us to travel a hundred times faster than we can today. Imagine it: thousands of inhabited planets at our fingertips. And we'll be able to explore those strange new worlds... and seek out new life and new civilizations. This engine will let us go boldly... where no man has gone before." The terminology and phrases Cochrane coined in this speech would be used in Starfleet for centuries to come. The speech would be revisited upon the launch of Enterprise, the first starship to benefit from the Warp Five engine. (ENT: "Broken Bow")