。
The walls are covered in graffiti.
Literal
Wall [topic-は] graffiti full-of is.
だらけ is a suffix meaning 'full of / covered in' — always with a negative connotation: 間違いだらけ (full of mistakes), 泥だらけ (covered in mud). 落書き is 'graffiti/scribbles.' The combination paints a picture of neglect or vandalism.