Routes around St Albans

My brother in law is quite new to cycling and has signed us both up to the london to windsor bike ride.I don’t think he has ridden much more than 20 miles so I thought I would meet him half way (st albans) and take him on a 40+ mile ride to see how he gets on before he breaks himself on a longer ride.

I know the area to drive around but not to cycle. Does anybody have any recommendations?

Thanks