Leisure attraction (9)
'leisure attraction' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for theme park that I've seen before include "number of visitors here?" , "Subject-based leisure attraction" , "In recreational area" , "Area with rides, displays, etc" , "Eg, Alton Towers" .)
(Another definition for themepark that I've seen is " Disneyland Paris, say".)