A secret backyard

There are three young hosts who don't like to maintain a frequent connection with the world outside the yard. For a couple of years, they have been immersing themselves in the backyard, spending time playing on their instruments.Their singing, which has been fluttering over the walls is so melodious that it has been attracting attention of the passers by. Of course, they can't help not to expect to enter the yard to have a look and listen. Unfortunately, the backyard doesn't open its door casually. Only the souls full of stories about the old times(?) are welcome to enter.