An important piece of Mesopotamian Mythology, and one of the oldest written stories. The story is about the goddess Inanna (later known as Ishtar) going to visit her sister (or possibly alter-ego) Ereshkigal.
Tropes in Inanna's Descent to the Netherworld include:
Evil Twin: Though it is not entirely clear which one is the evil one. See below.
Expy: Ereshkigal is a Darker and Edgier version of her younger twin, Inanna. Some scholars believe they were at one point two aspects of the same goddess before becoming separate entities.
Faux Action Girl: Inanna. She has to be rescued by her priestess and a male deity. However, this may have been a gambit of sorts. She had already sent out word of her demise ahead of time to her most powerful family members, knowing that no one who was in the underworld could break free on their own.
Just So Story: Explains why we have winter and summer. Inanna, the fertility goddess, lets everything go dormant when her beloved husband is down in the Underworld, and lets things grow in the summer when he's back and she's happy.
Laser-Guided Karma: Inanna loses her husband for half the year because she tried to steal Ereshkigal's husband Gugalana in The Epic of Gilgamesh only for him to get killed by Gilgamesh and Enkidu and tried to steal Ereshkigal's power.
MacGuffin: Asu-shu-namir, the asexual creatures that help Inanna be brought back to life.
My God, What Have I Done?: After Inanna's fury subsides and she realizes the horrible consequences of sicking demons after her husband, she weeps.
Not So Different: Inanna and Ereshkigal. In fact, Ereshkigal might actually be a Darker and EdgierExpy of Inanna. This is further supported by the interesting thematic relation of the husbands of both women dying in the story as bookends, as well as the link-up between this story and the story where Gilgamesh kills Inanna's bull of heaven (the exact same bull that is the husband of Ereshkigal).
Oral Tradition: The story was clearly this before it was recorded, as evidenced by the repetition.