Whilst it doesn’t feel that Super Mario Odyssey has a bunch of Kingdoms, you’ll soon realise that this isn’t the case. There’s 18 kingdoms in total. 15 that you unlock through progressing through the story, one that you unlock by completing the story (Mushroom Kingdom) and another two that you unlock by completing 250 (Dark Side) and 500 (Darker Side) power moons.
It’s well worth going back to each of he Kingdoms time and time again as more Power Moons will unlock and the world will be ever changing. It’s also well worth completing both Dark Side and Darker Side as both will give you a special unlock that’s only available by completing these levels