One of course must visit the Colosseum when they are in Rome. I have been here twice and both times the size and structure has amazed me. Rome is also a fantastic city where one can constantly find new interests around every bend.
It's now possible to tour the hypogeum, or underground spaces, beneath the Colosseum. Wandering among the ancient arches beneath the partially reconstructed forum floor really gives you a sense of the massive undertaking it was to put on the horrible spectacles above. The gladiators' tunnel, trap doors, elevators and animal cages are all given great context.
The Colosseum is on most tourists' bucketlist of things to see while in Rome. An impressive structure that is nestled between a combination of old ruins and new complexes, Rome's appreciation for their past is evident. So much history is preserved in the bustling city.
The Colosseum is remarkably old with the construction finishing in 80 AD. That's nearly two thousand years old. The structure itself was a grand theatre meant to be the center of Roman life by providing entertainment. Often grisly battles were fought between men, animals, and what have you. The structure today stands only partially after much wear and tear. Visitors can even peer into the basement corridors due to the partially destructed floors.