Data centers are typically shrouded in secrecy because they are the brains behind tech companies.

Google says when you're on a Google website, you're accessing one of the most powerful server networks in the known Universe.

Google has been working on building its data centers for over 10 years. The search giant's centers are efficient, take advantage of renewable energy, and are as environmentally friendly as possible.

The following tour is a glimpse inside a few of Google's data centers, which it calls the "physical internet".