An acropolis is like a big hill with buildings on top of it. Imagine you were playing with your toys and you built a big hill out of blocks or Legos. Then on top of that hill, you put your favorite toy buildings. That's kind of like what an acropolis is.
In ancient Greece, an acropolis was a really important place. It was usually in the center of the city and had important buildings like temples, palaces, and government buildings on it. People would go there to worship their gods, trade, and talk to their rulers.
To get to the top of the acropolis, they had to climb up stairs or a winding path. It was a really special place to be because you could see everything that was going on in the city from up there.
Even today, some cities in Greece still have their acropolises, and people like to visit them to see what they were like a long time ago.