The Copenhagen Marathon starts and finishes on Island Brygge while its route lies around the city's famous attractions like the Parliament Building, the Royal Palace, and the Little Mermaid. It also lies through the city's parks. Due to the flat surface, it might be easier compared to other routes, so it's good for first-timers.
The Copenhagen Marathon has around 9000 finishers among which you'll find people of all ages and genders. And, of course, be prepared to see some weird costumes.