expression, noun, noun which may take the genitive case particle 'no'
remote past; time immemorial
Refers to a time very long ago, often with a nostalgic or legendary feel. Used as a noun or with の to modify another noun.
遠い昔、この町には大きな城があった。
In the remote past, there was a large castle in this town.
それは遠い昔の話だ。
That's a story from time immemorial.
Compound of 遠い (とおい, 'far, distant') and 昔 (むかし, 'old times, long ago').