The description of the Fiend-patron warlock's Hurl Through Hell feature says:
Starting at 14th level, when you hit a creature with an attack, you can use this feature to instantly transport the target through the lower planes. The creature disappears and hurtles through a nightmare landscape.
At the end of your next turn, the target returns to the space it previously occupied, or the nearest unoccupied space. If the target is not a fiend, it takes 10d10 psychic damage as it reels from its horrific experience.
What happens if a Warlock uses their Hurl Through Hell ability... while in any of the lower planes? Does the target still make the trip through the other planes... possibly with an interlude directly overhead? Or, since they're already in a lower plane, do they stay put?
Related to, but distinct from, How does Hurl Through Hell work in Mechanus? (which was about whether Mechanus' averaging of rolls affected the damage).