Second round - Jonah 3

Then the word of the Lord came to Jonah a second time: “Go to the great city of Nineveh and proclaim to it the message I give you.”
Jonah 3:1-2

Now Lord spoke slightly differently from the first round when He had said
“Go to the great city of Nineveh and preach against it, because its wickedness has come up before me.”
Jonah 1:2

Wickedness of a city reaching the abode of God is a theme also in the case of Sodom and Gomorrah from which "outcry has reached me":

Then the Lord said, “The outcry against Sodom and Gomorrah is so great and their sin so grievous that I will go down and see if what they have done is as bad as the outcry that has reached me. If not, I will know.” 
Gen 18:20-21

This time Jonah obeyed the word of the Lord and went to Nineveh.


END IS NEAR!
Now Nineveh was a very large city; it took three days to go through it. Jonah began by going a day’s journey into the city, proclaiming, “Forty more days and Nineveh will be overthrown.” 

Jonah 3:3-4

A huge city, a New York of its time, and a single stranger walking and carrying a placard End is near!

But as Jonah had been afraid from the beginning his preaching was not ridiculed and ignored but taken very seriously:

Great city repents
The Ninevites believed God. A fast was proclaimed, and all of them, from the greatest to the least, put on sackcloth.
Jonah 3:5

As an external sign of repentance from evil and wickedness the people follow the public call for a fast, a kind of Ramadan in Nineveh, and put on sackcloth. 

שׂק saq

properly a mesh (as allowing a liquid to run through), that is, coarse loose cloth or sacking (used in mourning and for bagging); hence a bag (for grain, etc.): - sack (-cloth, -clothes).

Strong's Hebrew Dictionary