Sand pits are now covered with the green panels (I guess same as ones in the stacks seen in the background here https://westnordost.de/p/232126.jpg)
No clue what it is, but it doesn't look like some sport amenity, and more like a construction site for quite some time now. 

Regarding railings - I agree that those seen in photos are some form of crowd/entrance control. But I recall something looking like a proper bicycle parking racks at the northermost part of car parking.