Need ideas for back yard

[Lipstick]

I have no ideas and little experience when it comes to filling up space in my yard. The back wall is roughly 70 feet long and there is about 3 feet of empty space between the back wall and the retaining wall in front of the lawn. The retaining wall is about 2 feet high.

There is nothing behind the wall but a street.

I am open to any and all ideas of how to fill this space.