Conversation so far:
When did the Golden Age begin?
Aquaman's first origin story was presented in flashback from his debut in More Fun Comics #73 (November 1941).
What happened in #73?
The story must start with my father, a famous undersea explorer.
Who was his father?
if I spoke his name, you would recognize it.
What was his father's name?
CANNOTANSWER.
What did his father do?
His greatest discovery was an ancient city, in the depths where no other diver had ever penetrated.
What city did he discover?
My father believed it was the lost kingdom of Atlantis.

Question: What did he find there?
Self-contained rewrite: What did Aquaman's father find in the lost kingdom of Atlantis?