basic play off so many other cultivation/fantasy novels. the key point being the MC gets left in a secret/mystic/forbidden/inheritance/etc land/small-world/dimension/grotto-heaven.
•MC could be fleeing and fall into/get chased/left for dead/thrown into it
•Could be a case of not being able to leave before it seals shut again
•could be a reincarnator who chooses to hide/stay there to avoid forthcoming issues
•could be a transmigrator who wakes in the body of someone killed there, or due to transmigration was left confused (or just didn't get memories) and thus didn't make it to exit before it seals
•or any of a multitude of other possibilities