The Apple Watch wasn’t just whipped together by Jony Ive’s design team and kicked out of the nest. Instead, it’s a collaboration of plenty of teams inside of Apple’s headquarters. ABC recently had a tour of one of Apple’s secret fitness facilities, where the firm tests out the watch’s health monitoring features.

ABC said the facility, which looks like it’s in an abandoned warehouse of sorts, is one of the most advanced of its kind in the world. The news outlet had one of the first looks inside the secret lair, which has been operating for about two years. Jeff Williams, Apple’s senior vice president of operations, said Apple employees have been working out in the lab for years, running, biking and more, typically outfitted with millions of dollars worth of sensors, and some without even knowing they were contributing to Apple Watch research.

The expensive gear allowed Apple to track exactly when an exercise routine begins, and to more accurately predict how many calories are burned during a specific physical exercise. The facility, which appears to look like a combo between a yoga room and a gym, is also outfitted with climate chambers to measure how exercise is affected depending on various temperatures and with varying degrees of humidity.

Williams told ABC said the facility has allowed Apple to create one of the “world’s largest pieces of data on fitness,” and that Apple is “just beginning.” And of course, fitness is just a piece of what the Apple Watch will offer consumers when it launches next month.

Hit the source for ABC‘s inside look.