Heaven and Hell

The descriptions of Heaven and Hell throughout the Quran are allegorical. The Quran tells us so whenever such descriptions occur as independent statements, not within a general subject:

The 'mathal' (example) of Paradise, which is promised to the reverent, is that of rivers flowing beneath and its food supply is everlasting as well as its shade. Such is the outcome of those who revered God while the outcome of the disbelievers is the fire. 13:35

The 'mathal' (example) of Paradise that is promised to the reverent is that of rivers of unpolluted water, and rivers of milk whose taste does not change, and rivers of wine that is pleasurable for the drinkers, and rivers of strained honey. They have all kinds of fruits therein and forgiveness from their Lord as opposed to those who abide forever in the fire where they are given boiling water to drink which tears up their intestines. 47:15

The word "mathal" (example/allegory) is used in these verses, to tell us that we should not take the descriptions that follow literally.

Linguistically, the word "mathal" in these verses could be removed and we would still have perfect sentences; this is because the descriptions of Heaven and Hell are allegorical.
What Heaven and Hell are really like is far beyond our comprehension, hence the need for an allegory.
How can one describe, for example, the taste of chocolate to a person who never tasted chocolate? An allegory will have to be used. The person has to wait to actually taste chocolate in order to know what chocolate tastes like. Whatever allegory we use to describe the taste of chocolate it can only approximate the actual taste.
The Quran provides important information about the differences between the joys and pleasures on earth and those granted to the believers in Paradise:

1- All the joys of the worldly life mean little and are dwarfed when compared to the joys and rewards of Paradise:

Say, "The enjoyments of this world mean little, while the Hereafter is far better for the reverent. You shall not incur the least injustice."

Are you satisfied with the worldly life over the Hereafter? The enjoyment of the worldly life will mean so little in the Hereafter.

All enjoyments we are given on earth are mere illusions:

The worldly life is no more than a deceptive enjoyment.

The pleasures we are given on earth are designed only for the duration of the worldly life:

Adorned for the people are the worldly pleasures, such as the women, children, hoarded piles of gold and silver, trained horsed, livestock and tilth. These are the enjoyments of the worldly life while at God lies the best haven.

The pleasures and rewards in Paradise are beyond our understanding and nothing like what we are given on earth:

No self knows what hidden delights await them as rewards for what they used to do.

For all the above, it was necessary for God to use allegories when speaking to us about
Paradise and its rewards.
Heaven already exists, since Adam and Eve were placed in it during their days of innocence (2:35).
We learn from Sura 55 that there are two "High Heavens" - one for the humans and one for the jinn, also two "Lower Heavens" - one for the humans and one for the jinn.

The High Heaven vs The Lower Heaven

There are profound differences between the High Heaven and the Lower Heaven. Allegorically, water in the High Heaven flows freely (55:50), while the water of the Lower Heaven needs to be pumped out (55:66).
Allegorically, the High Heaven has all kinds of fruit (55:52), while the Lower Heaven has a limited variety of fruits (55:68).
Allegorically, the pure spouses readily join their spouses in the High Heaven (55:56), while the dwellers of the Lower Heaven must go to fetch their spouses (55:72).
Yet, even the Lower Heaven is an incredibly fantastic prize for those who are fortunate enough to escape Hell and end up in the Lower Heaven (3:185). People who depart this life before reaching their 40th birthday, and did not sufficiently develop their souls, will go to the Lower Heaven (46:15). The High Heaven is reserved for those who believed, led a righteous life, and developed their souls sufficiently.

Whoever is nudged away from the fire, and admitted into Paradise, has indeed won. 3:185