Steps leading to the observation deck on top of the Temple Mound.
You can read more on the history of the area here.
"The tallest and most impressive mound on the site is referred to as the First Temple Mound. Early Accounts of the large platform mound describe it as a large shell heap from the top of which one could see the Gulf of Mexico.
According to C.B. Moore's 1903 description, the mound stood 28 feet 8 inches high, with its summit plateau measuring 107 feet in length and 50 feet wide. A shell ramp, measuring 80 feet long and some 14-21 feet wide extended to the northeast across a shell causeway.
The causeway led towards the burial area and a marker stone. Because of its ramp and flat top, the mound gave every appearance of the typical temple mound often associated with later prehistoric cultures of the Southeast."
Source Florida State Parks