Gilgamesh.

There are two tablets included in the Epic of Gilgamesh that describe the Underworld.

• Tablet VII
• Tablet XII

Tablet VII:
Outline -

The gods decide that one of the heroes must die for slaying the Bull of Heaven and Humbaba. Despite the protestations of Shamash, Enkidu is marked for death. Enkidu considers the great door he fashioned for Enlil's temple, and curses it. He also curses Shamhat and the trapper for removing him from the wild. Then Shamash speaks from heaven, reminding Enkidu of how Shamhat fed and clothed him, and introduced him to Gilgamesh. Gilgamesh will bestow great honors upon him at his funeral, and will later wander the wild consumed with grief. Enkidu regrets his curses and blesses Shamhat, temporarily calmed. In a second dream, however, he sees himself being taken captive to the Netherworld by a terrifying Angel of Death. The underworld is a "house of dust" and darkness whose inhabitants eat clay and are clothed in bird feathers, supervised by terrifying beings. For twelve days, Enkidu's condition worsens. Finally, after a last lament that he could not meet a heroic death in battle, he dies.

This text is used to justify the idea that the Sumerian view of life after death is grim. 

The translation from Stephanie Dalley's Myths From Mesopotamia reads as follows:

Enkidu says "Listen my friend! I had a dream in the night. The sky called out, the earth replied, I was standing in between them.

There was a young man, whose face was obscured.

His face was like that of an Anzu-bird. He had the paws of a lion, he had the claws of an eagle. He seized me by my locks, using great force against me.

I hit him, and he jumped like a keppu-toy. He hit me and forced me down like an [onager?]. Like a wild bull he trampled on me, he squeezed my whole body.

(I cried out) "Save me my friend, don't desert me!" But you were afraid, and did not help me...

3 broken lines...

[He hit me and] I turned into a dove. [...missing words...] my arms, like a bird. He seized me, drove me down to the dark house, dwelling of Erkalla's god, to the house which those who enter cannot leave, on the road where traveling is one way only, to the house where those who stay are deprived of light, where dust is their food, and clay their bread.

They are clothed, like birds, with feathers, and they see no light, and they dwell in darkness.

Over the door [and the bolt, dust has settled.] I looked at the house that I had entered, and crowns were heaped up. I [...missing...] those with crowns who had ruled the land from time immemorial, [Preists (?) of] Anu and Ellil regularly set out cooked meats, set out baked (bread) set out cold water from waterskins.

In the house of dust that I had entered dwelt the enu and lagaru priests, dwelt the isippu and lumahhu-preists, dwelt the gudapsu-preists of the great gods, dwelt Etana, dwelt Shakkan, dwelt Ereshkigal, the Queen of Earth.

Belit-seri, the scribe of Earth was kneeling before her. She was holding [a tablet] and kept reading aloud to her.

She raised her head and looked at me: "[Who (?)....] brought this man"

There is a gap of fifty lives and when the translation begins again, Gilgamesh is reassuring Enkidu that the dream is a good sign.

Notes:

• Anzu-bird (Sumerian Imdugud, previously read Zu in Akkadian. Also pronounced Azzu) lion-headed eagle, born in the mountain of Hehe. Portrayed as wicked theif in Anzu, but benevolent in the Sumerian epic of Lugalbanda. Often shown in iconography in the pose of 'master of animals.
• keppu-toy possibly a whipping top, a spinning top made to spin by being whipped.
• Erkalla the land of the dead, also: Irkalla, Arali, Kigal, Gizal, Ganzar..
• Etana the twelfth king of Kush, after the flood.
• Shakkan Also called: Sumuqan and Amakandu -god of cattle and of herdsmen, often paired with Ashnan the grain god. Also pronounced Shahhan.

Tablet XII:
Outline -

This tablet is to a large extent an Akkadian translation of an earlier Sumerian poem, Gilgamesh and the Netherworld (also known as "Gilgamesh, Enkidu, and the Netherworld" and variants), although it has been suggested that it is based on an unknown version of that story. The contents of this last tablet are inconsistent with previous ones: Enkidu is still alive, despite having been killed off earlier in the epic. Because of this, its lack of integration with the other tablets, and the fact that it is almost a copy of an earlier version, it has been referred to as an 'inorganic appendage' to the epic. Alternatively, it has been suggested that "its purpose, though crudely handled, is to explain to Gil-gamesh (and the reader) the various fates of the dead in the Afterlife" as "an awkward attempt to bring closure",

Gilgamesh complains to Enkidu that various objects he possessed (the tablet is unclear exactly what — different translations include a drum and a ball) fell into the underworld. Enkidu offers to bring them back. Delighted, Gilgamesh tells Enkidu what he must and must not do in the underworld in order to come back. Enkidu does everything he was told not to do. The underworld keeps him. Gilgamesh prays to the gods to give him his friend back. Enlil and Suen don’t bother to reply but Ea and Shamash decide to help. Shamash cracks a hole in the earth and Enkidu's ghost jumps out of it. The tablet ends with Gilgamesh questioning Enkidu about what he has seen in the underworld.

The next text (XII) explains that life after death is better for those who have relatives in the world of the living to make offerings to their ghosts, that it is better to have married and to have left seven children (!) than remained childless and single. It is the same message Siduri, the barmaid at the end of the world, gives to Gilgamesh.

The translation from http://www-etcsl.orient.ox.ac.uk/section1/tr1814.htm reads as follows:

At the gate of Ganzer, in front of the nether world, he sat down. Gilgamec wept, crying bitterly: "O my ellag! O my ekidma! O my ellag, I am still not satiated with its charms, the game with it has not yet palled for me! If only my ellag waited still in the carpenter's house for me! I would treat the carpenter's wife like my own mother -- if only it waited still there for me! I would treat the carpenter's child like my little sister -- if only it waited still there for me! My ellag has fallen down to the nether world -- who will retrieve it for me? (1 ms. has instead: Who will retrieve my ellag from the nether world?) My ekidma has fallen down to Ganzer -- who will retrieve it for me? (1 ms. has instead: Who will retrieve my ekidma from Ganzer?)"

His servant Enkidu answered (1 ms. has instead: said to) him (1 ms. has instead: Gilgamec): "My king, you weep; why does your heart worry? Today I shall retrieve your ellag from the nether world, I shall retrieve your ekidma from Ganzer." Gilgamec answered Enkidu: "If today (1 ms. has instead: If) you are going to go down to the nether world, let me advise you! My instructions should be followed. Let me talk to you! Pay attention to my words (1 ms. has instead: My words should be followed)!

"You should not put on your clean garments: they would recognise immediately that you are alien. You should not anoint yourself with fine oil from a bowl: they would surround you at its (1 ms. has instead: your) scent. You should not hurl throw-sticks in the nether world: those struck down by the throw-sticks would surround you. You should not not hold a cornel-wood stick in your hand: the spirits would feel insulted by you. You should not put sandals on your feet. You should not shout in the nether world. You should not kiss your beloved wife. You should not hit your wife even if you are annoyed with her. You should not kiss your beloved child. You should not hit your son even if you are annoyed with him. The outcry aroused would detain you in the nether world."

"She who lies there, she who lies there, Ninazu's mother who lies there -- her pure shoulders are not covered with a garment, and no linen is spread over her pure breast. She has fingers like a pickaxe, she plucks her hair out like leeks."

Enkidu, however, did not heed not his master's words. He put on his clean garments and they recognised that he was alien. He anointed himself with fine oil from a bowl and they surrounded him at its scent. He hurled throw-sticks in the nether world and those struck down by the throw-sticks surrounded him. He held a cornel-wood stick in his hand and the spirits felt insulted by him. He put sandals on his feet. He caused irritation in the nether world. He kissed his beloved wife and hit his wife when he was annoyed with her. He kissed his beloved child and hit his son when he was annoyed with him. He aroused an outcry and was detained in the nether world.

Warrior Gilgamec, son of Ninsumun, directed his steps on his own to E-kur, the temple of Enlil. He cried before Enlil: "Father Enlil, my ellag fell down into the nether world, my ekidma fell down into Ganzer. Enkidu went down to retrieve them but the nether world has seized him. Namtar did not seize him, the Asag did not seize him; but the nether world has seized him. The udug demon of Nergal, who spares nobody, did not seize him, but the nether world has seized him. He did not fall in battle on the field of manhood, but the nether world has seized him." Father Enlil did not stand by him in the matter, so he went to Eridug.

In Eridug he directed his steps on his own to the temple of Enki. He cried before Enki: "Father Enki, my ellag fell down into the nether world, my ekidma fell down into Ganzer. Enkidu went down to retrieve them but the nether world has seized him. Namtar did not seize him, the Asag did not seize him; but the nether world has seized him. The udug demon of Nergal, who spares nobody, did not seize him, but the nether world has seized him. He did not fall in battle on the field of manhood, but the nether world has seized him." Father Enki stood by him in this matter.

He said to the young warrior Utu, the son born by Ningal: "Open a hole in the nether world immediately, and then bring up his servant from the nether world!" He opened a hole in the nether world and brought up his servant with his breeze (?) from the nether world.

They hugged and kissed. They wearied each other with questions:

"Did you see the order of the nether world? -- If only you would tell me, my friend, if only you would tell me!" "If I tell you the order of the nether world, sit down and weep! I shall sit down and weep! ......, which your heart rejoiced to touch, is ......, worms infest it like an old garment (?); like ...... of (?) a crevice, it is full of dust." "Alas!" he said and sat down in the dust.

"Did you see him who had one son?" "I saw him." "How does he fare?" "He weeps bitterly at the wooden peg which was driven into his wall." "Did you see him who had two sons?" "I saw him." "How does he fare?" "He sits on a couple of bricks, eating bread." "Did you see him who had three sons?" "I saw him." "How does he fare?" "He drinks water from a saddle waterskin." "Did you see him who had four sons?" "I saw him." "How does he fare?" "His heart rejoices like a man who has four asses to yoke." "Did you see him who had five sons?" "I saw him." "How does he fare?" "Like a good scribe he is indefatigable, he enters the palace easily." "Did you see him who had six sons?" "I saw him." "How does he fare?" "He is a cheerful as a ploughman." "Did you see him who had seven sons?" "I saw him." "How does he fare?" "As a companion of the gods, he sits on a throne and listens to judgments."

"Did you see the palace eunuch?" "I saw him." "How does he fare?" "Like a useless alala stick he is propped in a corner." "Did you see the woman who never gave birth?" "I saw her." "How does she fare?" "Like a ...... pot, she is thrown away violently, she gives no man joy." "Did you see the young man who never undressed his wife?" "I saw him." "How does he fare?" "You finish a rope, and he weeps over the rope." "Did you see the young woman who never undressed her husband?" "I saw her." "How does she fare?" "You finish a reed mat, and she weeps over the reed mat." "Did you see him who had no heir?" "I saw him." "How does he fare?" "Like him who ...... bricks (?), he eats bread." "......?" "I saw him." "How does he fare?"
7 lines fragmentary or missing

"Did you see ......?" "His food is set apart, his water is set apart, he eats the food offered (?) to him, he drinks the water offered (?) to him." (1 ms. adds: "Did you see him who was eaten by a lion?" "He cries bitterly "O my hands! O my legs!" ""Did you see him who fell down from the roof?" "They cannot ...... his bones.") "Did you see the leprous man?" "He twitches like an ox as the worms eat at him." "Did you see him who fell in battle?" "I saw him." "How does he fare?" "His father and mother are not there to hold his head, and his wife weeps." "Did you see the spirit of him who has no funerary offerings?" "I saw him." "How does he fare?" "He eats the scraps and the crumbs ...... tossed out in the street." "Did you see him hit by a ship's board (1 ms. adds: when diving (?))? How does he fare?" ""Alas, my mother!" the man cries to her, as he pulls out the ship's board ......, he ...... cross beam ...... crumbs." "Did you see my little stillborn children who never knew existence?" "I saw them." "How do they fare?" "They play at a table of gold and silver, laden with honey and ghee." "Did you see him who died ......?" "I saw him." "How does he fare?" "He lies on a bed of the gods." "Did you see him who was set on fire?" "I did not see him. His spirit is not about. His smoke went up to the sky."

Note:
In the Sumerian version the deity who brings Enkidu's ghost back, is the sun- Utu. In the Akkadian version  added as a twelfth tablet to the Epic of Gilgamesh, the rescuer is Nergal: written U.GUR


From Dr Gwendolyn Leick:
GIR.UNU.GAL doesn't seem to be originally Sumerian

To the Akkadians it may have sounded like sounded like ne.eri.gal (lord of the great below).