The Underworld (Gilgamesh)

Travel to the underworld is only for the most dedicated voyager, as the trip is fraught with peril and requires hard work. For those who make it all of the way to the end, the reward is immortality. Those who cannot complete the challenge are returned home in their sleep and given moldy bread.

The voyage begins at the mouth of the cave through the Dark Mountain. The traveler must pass through the mountain, on foot, in complete darkness. This portion of the journey requires 24 hours of non-stop walking. It’s worth the effort, though.

And check out that view.

The cave empties out onto a garden paradise that lies on the shore of a vast and treacherous ocean. The garden is always in bloom, and the scent of thousands of exotic flowers combines with the song of thousands of birds to fill the air with beauty. On the shore of the ocean is a tavern, run by Siduri. Here, the traveler may eat and drink his fill. Siduri will advise you to return home and not continue with the voyage, as it involves crossing the ocean. Should you not heed her advice, she will direct you to the boatman, who lives in a nearby wood. He is called Urshanabi. If you want him to help you to cross, you must build a raft of 120 (or 300) long poles. The crossing is so perilous that the raft will break up upon arrival on the other shore. Only the most spry tourists should take this journey, as touching the water will kill you, so a well-timed leap is essential.

Only now will the traveler meet the tour guide to the underworld, Utnapishtim, survivor of a large, world-destroying flood.

He made a large boat and filled it with animals. 

No apparent similarities to any other story.

 He will present you with a challenge: if you can stay awake for seven days straight, you will be granted immortality. Should you fall asleep, he will return you to your home, and as proof of your sleeping, will place a loaf of bread by your bed for each day you sleep. You only get one shot at the challenge. Trips to this world are strictly limited to one per life-time.