“…then the good son of Iapetus stole it back for mortals from Zeus the counsellor, in a hollow fennel stalk, unseen by the Thunderer.”
The hint
Fire was carried out of heaven hidden in a hollow stalk. What survives the carrying is small, and it is enough. Every hall opens with the same key. Three steps back.
The cipher
HPEHU
— Hesiod · Works and Days · c. 700 BCE
Enter this door
Your email to attempt the solve. One win per solver across the run.