We all have this,
we all have kitchens in our homes
yet one can easily miss.
only those who know of it's whereabouts know the exact place
A secret you will have to know,
to very few I show.
the fruit bowl painting and tickling the pear,
Many unseen I hold,
the house-elves work in the kitchen but are never seen around the school
Don't offend you are told
Hermione started talking of freedom for the elves and they didn't like it so they rushed the trio out after giving them food
CLUE:
I see two and two from my end,
Fred-George and Dobby-Winky, the people trio met trio on talking about the kitchen then visiting
One let slip one is seen, this is the clue i send.
The twins slip the whereabouts to hermione and Dobby-Winky were the elves we saw before the visit.
Answer: THE HOGWARTS KITCHEN!!!