Naraka or Svarga are lokas, AND also relative to the person experiencing them i.e. you can experience misery in heaven or bliss in hell, or either one on earth itself, depending on your karma and viewpoint.
In Mahabharata, Yayati, after being pushed down by Indra from Svarga, talks to Rishis:
Yayati answered, 'O pious one, they that speak of their own merits are
doomed to suffer the hell called Bhauma. Though really emaciated
and lean, they appear to grow on Earth (in the shape of their sons and
grandsons) only to become food for vultures, dogs, and jackals.'
Ashtaka said, 'When life is destroyed with age, vultures, peacocks,
insects, and worms eat up the human body. Where doth man then reside?
How doth he also come back to life? I have never heard of any hell
called Bhauma on Earth!'
Yayati answered, 'After the dissolution of the body, man, according to
his acts, re-entereth the womb of his mother and stayeth there in an
indistinct form, and soon after assuming a distinct and visible shape
reappeareth in the world and walketh on its surface. This is that
Earth-hell (Bhauma) where he falleth, for he beholdeth not the
termination of his existence and acteth not towards his emancipation.'
Note - the English/Abrahamic terms hell and heaven are similar to narak and svarg in Hinduism. The main difference is that narak and svarg and bhumi are all permanently temporary (they get created & destroyed cyclically, and also people travel between these 3 lokas cyclically), whereas Christian/Islamic hell and heaven are said to be permanent.
In Hinduism, only Moksha is said to be permanent.