Does Key West have pryamids or zuggurat appearing structures?

I woke up yesterday and asked my girlfriend if she wanted to drive down to the Florida Keys for the day. She agreed and so we headed south until the Florida turnpike ended and we were on US1 then we keep going and going until the straight road turned into a T in Key West and I hung a right. We drove down past MILE 0 on US1 and continued to explore, enjoying the older buildings and homes in the area. All of a sudden, we came across a fenced in area that had two man made hills that were pyramid shapped and had concrete steps down one side, almost similar to the Aztec Zuggurats (or pyramids) I have seen in Mexico. I looked around for someone to ask, but it did not appear to be too great of an area to be hanging around in, so I turned around and headed back to where the tourists hang out and we hit a couple bars and had a great time. Today, I am wondering what kind of structures we came across. Maybe it was some kind of land fill. If anyone knows, please fill me in...thanks