The National Security Agency has turned Germany into its most important base of operations in Europe, according to a story published by Der Spiegel this week.

The German magazine reports that documents provided by NSA whistleblower Edward Snowden “paint a picture of an all-powerful American intelligence agency that has developed an increasingly intimate relationship with Germany over the past 13 years while massively expanding its presence.” The magazine adds, “No other country in Europe plays host to a secret NSA surveillance architecture like the one in Germany…In 2007, the NSA claimed to have at least a dozen active collection sites in Germany.”

The story reveals that the NSA’s key facilities in Germany include Building 4009 at the “Storage Station” on Ludwig Wolker Street in Wiesbaden, which is in the southwest of the country. Officially known as the European Technical Center, the facility is the NSA’s “primary communications hub” in Europe, intercepting huge amounts of data and forwarding it to “NSAers, warfighters and foreign partners in Europe, Africa and the Middle East,” according to the documents.