The recent fine weather made this a must for us. We usually park the car in King Harry Lane, opposite the Waitrose supermarket, and then stroll across the Park, taking in the excellent views of the Cathedral and surrounding area.
The city itself is an interesting place, plenty of old character properties (Fishpool Street is a good example) and of course the Cathedral is a must-see. There was a small Magna Carta exhibition there when we visited, with one of the original documents on display. Admission charge but well worth it.
Any number of lunch places here, in good weather we like to sit outside one of the cafés in the narrow streets and watch the world go by.
If you're interested in the ancient history aspect, you have the Verulamium Museum, the Hypocaust, and the Roman Theatre just the other side of Bluehouse Hill.
Young families are also well catered for in the Park, so there is something for everyone here.
We're very fortunate to be living just a short drive away, and a stroll around the Park costs nothing. For anyone not familiar with the area, it's worth mentioning that on Sundays you can park in the city centre multi-storey free of charge.