Fantastic old people's tombs (7)

I believe the answer is:

dolmens

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'tombs' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe they are linked in a way I don't understand?

'fantastic old people's' is the wordplay.
'fantastic' indicates anagramming the letters (a fantastic or improbable ordering of the letters).
'people's' becomes 'mens' (men are people).
'old' is an anagram of 'dol'.
'dol'+'mens'='DOLMENS'

Can you help me to learn more?

(Another definition for dolmens that I've seen is " gravestones".)

I've seen this clue in The Times.

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