Giunsero alfine al loco in cui discese
Fiamma dal cielo in dilatate falde,
E di natura vendicò l'offese
Sovra le genti in male oprar sì salde;
Fu già terra feconda, almo paese,
Hor acque son bituminose e calde,
E steril lago; e quant'innonda e gira,
Compressa è l'aria e grave odor vi spira.
They reached the place where a fire
Once fell from heaven in large layers,
Thus punishing the sins against nature
On those people so addicted to evildoing.
It had been a fertile land, mother of life;
Now, only hot and bituminous waters,
A barren lake; all around its perimeter
The air is heavy, full of a foul smell.
The knights who follow Armida do not actually reach her alleged "city," but her own enchanted castle on the banks of the Dead Sea. Renaissance and later maps (e.g. in Christian Adrichom, The Twelve Tribes of Israel, 1628) even reported the position of Sodom under the lake's surface.
To strengthen the hellish atmosphere, Tasso inserts some quotations and echoes from Dante, see Inferno 14: 29, 6: 15, 9: 31.