What you see is the culmination of one man’s work over the course of 15 years now named the Philadelphia Magic Gardens.
From their website:

“[Isaiah] Zagar started working on the Magic Gardens in 1994 in the vacant lot nearby his studio. He began by constructing a massive fence to protect the area from harm and then spent the next fourteen years excavating tunnels and grottos, sculpting multi-layered walls, and tiling and grouting the 3,000 square foot space. The installation pays tribute to Zagar’s many artistic influences, as well as the events and experiences of his life. Enveloped in visual anecdotes, the mosaicked walls refer to his wife Julia and sons Ezekiel and Jeremiah through playful images and words, but also reference important elements of the wider world. Las Pozas and Day of the Dead, the dance community of Philadelphia, and even the airplanes of the nationwide 9/11 tragedy.