The most common and most likely answer to this crossword clue is the 11 letter word ATTRACTIONS
A
T
T
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Buddy explains!

The straight part
We know that "fantastic sights" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fantastic sights = attractions.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.
Crossword Answer definitions
ATTRACTIONS noun- The tendency to attract.
- The feeling of being attracted.
- An event, location, or business that has a tendency to draw interest from visitors, and in many cases, local residents.
- The sacrifice of pieces in order to expose the enemy king.