We’ve passed the Pyramid of Caius Cestius on taxi trips from Rome airport, but were determined to see it up close. It’s an easy trip from the Colosseo to Piramide metro station. The Pyramid is immediately viewable when you pop back up above ground.
The tomb remains well-preserved because it was built into the Aurelian Wall circuit in the third century CE (and because it’s recently been restored due to philanthropic funding). Later post-Classical generations would forget its original use and it came to be thought of as the Tomb of Romulus. It’s definitely not that old – it was actually built in the first century BCE, when all things Egyptian were in vogue, as the final resting place for Caius Cestius. He was a magistrate and a member of a religious order, as the Latin inscription notes.
My favourite views of the monument came from the Protestant Cemetery side. It’s a peaceful background to the grave of Keats in particular.
It’s also possible to get inside the Pyramid to see its frescoes, although opening hours are limited.