A showpiece is something that is the best example of its kind, often put on display to be admired.
A showpiece is something special and impressive, like a treasure or a work of art.
Examples:
The diamond necklace was the showpiece of the collection.
The cake was a showpiece at the party.
The showpiece of the museum was a big painting.
The showpiece of the show was a dancing dog!
The showpiece of the garden was a giant flower sculpture.
The showpiece of the concert was a very famous singer.