The Circus Maximus in Rome is an ancient chariot racing stadium and mass entertainment venue with a long and storied history. It was the first and largest stadium of its kind in Ancient Rome and its empire, spanning 621 m (2,037 ft) in length and 118 m (387 ft) in width and able to accommodate more than 150,000 spectators. Over the centuries, it became the model for circuses throughout the Roman Empire and hosted a variety of events—from chariot races and track athletics to public executions and grand religious processions. Even today, after centuries of disuse, the Circus Maximus remains a popular tourist destination; it is now a public park and offers visitors a glimpse into the glory days of Ancient Rome. It's used for several events like concerts that take place in this historical location.

The history of Circus Maximus is really fascinating, but if you are expecting to see something like the Colosseum, you might be disappointed. All that remains today is a few ruins and it's mostly a large park.

I'd include Circus Maximus in a walk from Colosseum to the Aventine hill, so you can still see it, but don't have to come here just for it.