Vacant rooms in Vienna possibly house celebrations (13)

I believe the answer is:

anniversaries

I'm a little stuck... Click here to teach me more about this clue!

'celebrations' is the definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.

'vacant rooms in vienna possibly house' is the wordplay.
'vacant' says to hollow out the word (remove centre letters) (a vacant or emptied out form of the word).
'in' means one lot of letters goes inside another.
'possibly' indicates an anagram.
'house' becomes 'aries' (Aries is an example).
'rooms' with its middle removed is 'rs'.
'vienna' is an anagram of 'annive'.
'annive'+'aries'='annivearies'
'rs' inserted within 'annivearies' is 'ANNIVERSARIES'.

Can you help me to learn more?

(Other definitions for anniversaries that I've seen before include "occasions" , "Significant dates" .)

I've seen this clue in The Independent.

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