The most common and most likely answer to this crossword clue is the 13 letter word INSTALLATIONS
I've seen this crossword clue in The Daily Telegraph
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Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INSTALLATIONS mean?
INSTALLATIONS noun- An act of installing.
- Something installed, especially the whole of a system of machines, apparatus, and accessories, when set up and arranged for practical working, as in electric lighting, transmission of power, etc.
- A work of installation art.
- A grouping of facilities that constitute a permanent military base.