(for those who disbelieve in their Lord is the torment of Hell, and worst indeed is that destination.) This means that this will be the worst end and a terrible destiny.
إِذَآ أُلْقُواْ فِيهَا سَمِعُواْ لَهَا شَهِيقًا
(When they are cast therein, they will hear its Shahiq) Ibn Jarir said, "This means the sound of shouting."
وَهِىَ تَفُورُ
(while it is simmering.) Ath-Thawri said, "It will boil them just as a small number of seeds are boiled in a lot of water." Then Allah says,
وَلَقَدْ زَيَّنَّا السَّمَاءَ الدُّنْيَا بِمَصَابِيحَ وَجَعَلْنَاهَا رُجُومًا لِّلشَّيَاطِينِ (And We have decorated the nearest sky with lamps, and have made them devices to stone the devils, and We have prepared for them the punishment of Hell....67:5). The word 'masabih' (translated above as 'lamps' ) stands for 'stars'. The fact that the sky is decorated with stars does not necessarily imply that they should be studded with them inside or under the sky. The decoration is available also to the situation when the stars are far below the sky in space as modern research has proved it by observation. This is not contradictory to the classical interpretation.
At various places in the Quran, the picture of hell has been drawn. Though this hell is not observable today by man, it can be seen indirectly and imagined through the meaningfulness of the universe. The fact is that if there were to be no reckoning of the evil people brought to account in the Hereafter, the entire meaningfulness of the universe would become inexplicable. The punishment of the Hereafter not being visible in the present world is precisely in accordance with God’s plan. It is the intention of God to select such persons as are convinced of His greatness and who obey Him without actually having seen Him. And the assessment of such people cannot be properly made unless the fate awaiting everybody in the Hereafter is kept out of their sight, so that whatever a man does here, he does out of free will and not under any compulsion.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.