The walls were built around 270 year. There are quite well-preserved remains of them, which can be seen as you explore the city.

There are various sections still available to see (in varying state of repair), but exploration simply means walking along its length coming across the occasional entrance arches or guard houses. Suggestion is to catch what you do as part of your normal sightseeing journeys - no special trip necessary.

I gave up on visiting the planned route because it was difficult to follow in places, but what I did see was quite interesting, purely because I was treading the route that Legionnaires and Centurions wad walked before me. I have to be honest and say that unless there is something in particular is your chosen point of interest, I wouldn't waste time on this as there are far more interesting things to see in Rome, if your time is precious.