The most common and most likely answer to this crossword clue is the 7 letter word PALAZZI
P
A
L
A
Z
Z
I
Buddy explains!
The straight part
We know that "impressive piles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impressive piles = palazzi.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 PALAZZI mean?
PALAZZI noun- A large, palatial urban building in Italy.