This is Hemliga Trädgården[a] (The Secret Garden) in Midsommarkransen. Despite its name, it's not all that secret - having a website and being bookable for parties and so on - but I'm surprised that no address is listed on their website.
The garden appears to be mostly aiming for the anti-capitalist-smash-the-system demographic, and I'm sure that we can have a good time trying to reconcile having to rent a place for the purpose of abolishing property rights. Another more sensible grouping that have used the Garden is "Hackerspacet Sparvnästet IRL men inte AFK", which in the language of their people means The "Sparrow's Nest" Hacker Space - In Real Life, but not Away From Keyboard, who spent some time doing firmware hacks of wireless network adapters under the motto
the air is free. To my great surprise, these people seemed actually reasonable; with no over-the-top rhetoric.