The Soviets had at least two closed towns near Berlin with at least part of their reason for existing being to keep a "friendly" eye on the city. These towns were off limits to Germans, self contained and were almost independent from East Germany in terms of food and supplies.
The first, Vogelsang, was a barracks town built by the Soviets in the village district of the same name. It lies just a little over 50km north from the centre of Berlin and had a tank division based there.
Vogelsang is particularly interesting because apparently during the course of its occupation by the Soviets, they stationed and/or stored nuclear missiles there on a few ocassions, the last being from 1983 till 1988.
Some links
http://www.bbc.com/news/magazine-20079147
http://www.uncubemagazine.com/blog/14820889
https://yearinberlin.com/2013/05/08/...et-ghost-town/
http://www.abandonedberlin.com/2014/...-missiles.html
This last two links may prove useful for this particular discussion as one is the website of an Englishman who spent time living in Berlin and exploring the city while the other is the site of an urban explorer devoted to Berlin.
The second town, Wünsdorf, was about 40km south of the centre of Berlin and was a Soviet headquarters town with a nearby airfield. Wünsdorf is particularly interesting because it was the site of the WW2 German regime's Maybach I and Maybach II high command bunkers (which were mostly destroyed by the Soviets but some buildings and bunkers were left intact and re-used by them). It had a rail link that ran directly to Moscow and was apparently the largest Soviet base outside the USSR (estimated at between 70,000 and 60,000 personnel).
The townsite has been somewhat re-purposed as a book sellers marketplace.
Some links
http://www.spiegel.de/international/...-a-800658.html
http://www.nytimes.com/1995/08/14/wo...potential.html
http://www.abandonedberlin.com/2013/...ans-lenin.html
https://lostandforgottenberlin.wordp...orf-waldstade/
Again, the last two links are particularly relevant to this discussion, although the first is already mentioned above. The second is also an urban explorer's site devoted to Berlin.
For anyone visiting the area in the future, tours of the town can be taken: -
http://www.buecherstadt.com/en/bunker/
http://www.hivino.travel/discover-ge...book-town/e407
Slightly off-topic but those links could also prove useful for anyone running the Contested Ground Studios rpgs
Hot War or more particularly
Cold City.
http://www.contestedground.co.uk/