I have been to Hitchin several times as Mr B has friends that live there. It is a nice market town. Great for a day out. I think you should tie coming here with a visit to Hitchin Lavender. Both are not a full day out and since it is a bit far from the Lakenheath/Mildenhall area but together can be very nice. There are some chain restaurants and small shops in Hitchin. In fact, I had our cake topper for our wedding made here.
There are several places where you can go to pick lavender and Hitchin Lavender is one of them. It costs £4.50 for a bag and you can go out in the fields and pick it yourself. The time for this is usually June to August. This will give you loads to make homemade soaps and the like. I put them in a little bag and put it in my pillow.
Graveley Fruit Farm
I happened to miss the PYO Strawberries in 2020, and found out about the Graveley Fruit Farm. It was only a 45 minute drive and if it hadn't been the year of Corona Virus, I think I would have arranged to do the Lavendar and this on the same day. But you have to book times for everything so I opted to do this only. The strawberries were delicious but it was a was a great day. They also have a sandpit and playground.
Radwell Meadows
We went here after the visit to the Graveley Fruit Farm but I was thinking about going here after the Hitchin Lavender because Bug likes just going for walks. Radwell Meadows came up on my search. We loved wandering around here after we had our lunch. Good option to combine with either places.