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.

Spiegel also reports that an even larger NSA facility is under construction three miles away, in the Clay Kaserne, which is a U.S. military complex. Called the Consolidated Intelligence Center, the facility will cost $124 million once it is completed, and will house data-monitoring specialists from the Storage Station.

The agency’s operations in Germany came under intense scrutiny earlier this year when Spiegel revealed that the NSA had eavesdropped on Chancellor Angela Merkel’s cellphone calls. In its latest issue, the magazine reports on a legal controversy over the NSA’s still-close relationship with its German partner, the Bundesnachrichtendienst (BND). The Snowden documents show that “the exchange of data, spying tools and know-how is much more intense than previously thought,” according to Spiegel—and this raises the question of whether the BND is violating constitutional protections on privacy for Germans abroad and foreigners in Germany.

The scope of the NSA’s activities in Germany is considerable. Another key NSA facility, Spiegel reports, is the “Dagger Complex” in Griesheim, a town about 25 miles from Wiesbaden. It is “the NSA’s most important listening station in Europe,” with around 240 intelligence analysts working there in 2011. The facility’s official name is the European Center for Cryptology. “NSA staff in Griesheim use the most modern equipment available for the analysis of the data streams, using programs like XKeyscore, which allows for the deep penetration of Internet traffic,” according to Spiegel.

The story also delves into the growth of facilities that house the NSA’s Special Collection Service, which is a joint operation with the CIA to collect targeted communications. There are more than 80 SCS stations around the world, and the Snowden documents indicate two sites are located in Germany—in the U.S. consulate in Frankfurt, and the U.S. embassy in Berlin, which is where the SCS is believed to have recorded Chancellor Merkel’s phone calls.