In The Netherlands, of course. This is the Hovenring under construction:
… this was an extremely large rural roundabout (officially a ‘traffic circle’ because of the right of way arrangements) with separated cycle paths all around it (map here, before the Hovenring) …
Now why did this have to change? It had cycle paths and there were traffic lights to control the flow of traffic. But to the Dutch that is not safe enough anymore. Yes, there was separation, but at the places of crossing motorized traffic and cyclists were only separated in time and not in place.
This elevated bike roundabout is 72 metres in diameter, with a 70-metre tall pylon. It opened on June 29, and this is how it was being used on Aug 12:
It looks like there are more bikes on the ring than cars on the motorway.