Rivers are a fundamental part of the topography of the underworld and are found in the earliest source materials: In Homer's Iliad, the "ghost" of Patroclus makes specific mention of gates and a river (unnamed) in Hades; in Homer's Odyssey, the "ghost" of Odysseus's mother, Anticlea, describes there being many "great rivers and appalling streams", and reference is made to at least four specific rivers. H. A. Guerber assumed that the rivers where Charon sailed mirrored the sky in Greco-Roman thought. In the wider mythological tradition, however, there are multiple bodies of water that are associated with the underworld (varying in number and combination depending on the source), the names of which can be understood to reflect specific associations with death.
• The Styx can be considered the most prominent and familiar of the underworld rivers. It is the only named underworld river mentioned in Homer's Iliad – our earliest mythological text – and three of the Homeric Hymns. Not only is it an underworld river but is also, more generally, the inviolable waters upon which the gods swear oaths and a goddess in her own right (the daughter of Oceanus and Tethys). In later traditions it often serves as the entrance to the underworld over which Charon (the ferryman of the dead) rows the deceased in order for them to enter the underworld. It is also known as the river of hatred. There are several Styx-es in the real world: according to Herodotus, Strabo, and Pliny it was in Arcadia; while Pausanias locates one in Nonacris.
• The Acheron is the river of misery or river of woe. It is mentioned in many early sources of archaic poetry but is less prominent and early than the Styx. In some mythological accounts, Charon rows the dead over the Acheron rather than the Styx. In some alternative sources Acheron is a lake (rather than/as well as the river) and also functions as a synonym for the underworld. Pausanias describes a river named Acheron in Epirus, Thesprotia, which flows into a swampy-lake and converges with a river Cocytus (like its Homeric counterpart) which Pausanias attributes as the inspiration for Homer's description of the underworld. This site is also associated with specific instances of necromantic ritual and/or catabases from the mythic-past. Likewise, later traditions note an Acheron river in Cumae, Italy, which was also identified specifically with Odysseus' necromantic/catabatic activity.
• The Pyriphlegethon/Phlegethon is the river of blazing-fire (Pyriphlegéthōn being from the phrase puri phlegethonti, 'blazing like fire'). It has a single mention in Homer's Odyssey (Pyriphlegéthōn) where it is described as flowing into the river Acheron, and then does not appear again in sources until Plato. According to Plato, this river leads to the depths of Tartarus and is associated with punishment (in particular, people who hit their fathers and mothers). There was a river/field of this name near Cumae – maintaining its association with 'burning' due to the local hot springs – which Strabo explicitly associated with the Homeric underworld.
• The Cocytus is the river of wailing (from kōkuein, 'to weep, lament'). It too has only a single mention in Homer's Odyssey where it is described as a branch of the Styx that flows into the Acheron. According to Plato, the Cocytus is circular and empties into Tartarus and is associated with the punishment of murderers. It is also the name of a river in Thesprotia and Cumae which merges with the Acheron (see above).
• The Lethe is the river of forgetfulness, taking its name from Lethe, the goddess of forgetfulness and oblivion. In later accounts, a poplar branch dripping with water of the Lethe became the symbol of Hypnos, the god of sleep. Some sources reference a plain of Lethe, rather than a river.

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In the Greek underworld, the souls of the dead still existed, but they are insubstantial, and flitted around the underworld with no sense of purpose. The dead within the Homeric underworld lack menos, or strength, and therefore they cannot influence those on earth. They also lack phrenes, or wit, and are heedless of what goes on around them and on the earth above them. Their lives in the underworld were very neutral, so all social statuses and political positions were eliminated and no one was able to use their previous lives to their advantage in the underworld.

The idea of progress did not exist in the Greek underworld – at the moment of death, the psyche was frozen, in experience and appearance. The souls in the underworld did not age or really change in any sense. They did not lead any sort of active life in the underworld – they were exactly the same as they were in life. Therefore, those who had died in battle were eternally blood-spattered in the underworld and those who had died peacefully were able to remain that way.

Overall, the Greek dead were considered to be irritable and unpleasant, but not dangerous or malevolent. They grew angry if they felt a hostile presence near their graves and drink offerings were given in order to appease them so as not to anger the dead. Mostly, blood offerings were given, because they needed the essence of life to become communicative and conscious again. This is shown in Homer's Odyssey, where Odysseus had to offer blood of sheep in order for the souls to interact with him. While in the underworld, the dead passed the time through simple pastimes such as playing games, as shown from objects found in tombs such as dice and game-boards. Grave gifts such as clothing, jewelry, and food were left by the living for use in the underworld as well, since many viewed these gifts to carry over into the underworld. There was not a general consensus as to whether the dead were able to consume food or not. Homer depicted the dead as unable to eat or drink unless they had been summoned; however, some reliefs portray the underworld as having many elaborate feasts. While not completely clear, it is implied that the dead could still have sexual intimacy with another, although no children were produced. The Greeks also showed belief in the possibility of marriage in the underworld, which in a sense implies the Greek underworld was little different from the world of the living.

Lucian described the people of the underworld as simple skeletons. They are indistinguishable from each other, and it is impossible to tell who was wealthy or important in the living world. However, this view of the underworld was not universal – Homer depicts the dead keeping their familiar faces.

Hades itself was free from the concept of time. The dead are aware of both the past and the future, and in poems describing Greek heroes, the dead helped move the plot of the story by prophesying and telling truths unknown to the hero. The only way for humans to communicate with the dead was to suspend time and their normal life to reach Hades, the place beyond immediate perception and human time.

The Greeks had a definite belief that there was a journey to the afterlife or another world. They believed that death was not a complete end to life or human existence. The Greeks hypothesized a soul after death, but saw the afterlife as meaningless. In the underworld, the identity of a dead person still existed, but it had no strength or true influence. Rather, the continuation of the existence of the soul in the underworld was considered a remembrance of the fact that the dead person had existed, yet while the soul still existed, it was inactive. However, the price of death was considered a great one. Homer believed that the best possible existence for humans was to never be born at all, or die soon after birth, because the greatness of life could never balance the price of death. However, it was considered very important to the Greeks to honor the dead and was seen as a type of piety. Those who did not respect the dead opened themselves to the punishment of the gods – for example, Odysseus ensured Ajax's burial, or the gods would be angered.