the next Skate-By-Night is this Wednesday (2.7. Protected content . I find it a different but fun way to explore the city. The get together is at 18:30 but it won't start before 20:30. Costs are 2€ but included are a drink at midway and as far as I know the costs if you want to rent skates. It is a sportive event but no way competitive. You can just try it and in the worst case there is a bus picking up the ones that are exhausted. Heard it is also fun to sit in that historic pickup bus!
So if you are interested it would be nice to get together and enjoy a fun night out!