Kingdom
Kingdoms are locations in Super Mario Odyssey which can be traveled to from the World Map, comparable to the "worlds" that are present in many other Super Mario games. There is a total of 17 kingdoms in the game, twice as many as other games in the series which mostly have 8 or 9 worlds. 14 of these kingdoms are part of the "main game", while Mushroom Kingdom, Dark Side and Darker Side are "post-game". Collectables that can be found in kingdoms include Power Moons and regional coins, with more common collectables such as regular coins being scattered throughout as well.
Accessing kingdoms
Most kingdoms require a certain number of Power Moons to be collected in the previous kingdom to be unlocked. This requirement is not present for Cap Kingdom, as it is the kingdom in which the game begins, Cascade Kingdom, because Cap Kingdom (which precedes Cascade Kingdom) does not contain any Power Moons during the first visit, and Mushroom Kingdom, which is unlocked upon finishing the Escape sequence in Moon Kingdom. The Dark Side and Darker Side of the Moon can be unlocked after getting to Mushroom Kingdom by reaching a total Power Moon count of 250 for the former and 500 for the latter. As Cloud Kingdom and Ruined Kingdom are not revealed to the player until traveling from Wooded Kingdom/Lake Kingdom and Luncheon Kingdom respectively, the total Moon counts of Wooded/Lake Kingdom and Luncheon Kingdom do not unlock Metro Kingdom and Bowser's Kingdom, even though it might not seem so until Cloud Kingdom and Ruined Kingdom are revealed on the world map.
Power Moon counts
Not all Power Moons that can be found in a kingdom are available upon first visiting the kingdom. This can be the case because some Power Moons may be inaccessible until peace is achieved in that kingdom, as well as Moon Rock moons only being obtainable after unlocking Mushroom Kingdom. This is closely related to scenarios, which are used by the game to determine which moons are enabled.