I read a book in 2017, I think; it was about a boy who, for the summer had to go to his grandparents estate in the forest.
I remember it was huge with gargoyles on the front gate. He finds a really tall wall surrounding an area and tries to find his way in. He gets in and does some things and accidentally hatches dragons.
His grandfather stayed in an observatory, and most rooms had no furniture.
I think the book had a blue dragon on the cover.