Ancient hotels had fluctuating misfortunes (3,2,3,5)
I believe the answer is:
old as the hills
'ancient' is the definition.
(I've seen this before)
'hotels had fluctuating misfortunes' is the wordplay.
'fluctuating' is an anagram indicator.
'misfortunes' becomes 'ills' (ill is a kind of misfortune).
'hotels'+'had'='hotelshad'
'hotelshad' with letters rearranged gives 'oldastheh'.
'oldastheh'+'ills'='OLD AS THE HILLS'
(Other definitions for old as the hills that I've seen before include "Ancient" , "antique" .)