The Leper Chapel of Saint Mary Magdalene — Attraction in Cambridge

Free to visit. It's only open on a small number of days each year (look at the website in advance), although you can get a very good idea of it from the outside (accessible at any time) and it's mostly rather plain inside (albeit with some interesting architectural details). Originally 12th century though it has been much repaired, rebuilt and altered over the centuries. It sits on a pleasant plot of green land just alongside Newmarket Road: you can easily park at one of the superstores nearby and walk there.

It's very small, so if you want to extend the visit then you can walk down to the river and on to Fen...

Fantastic mediaeval building from around 1125 and is the second oldest complete building in Cambridge. In 1211 king John granted charter allowing a three day market on the vigil of Holy Cross. It survived due to its association with the Stourbridge Fair. You need to walk to it as there is no parking nearby but...

Exquisite, ancient Romanesque-style chapel well outside the city's main tourist areas. You'll most likely have it to yourself if you make the fairly small effort (it's on a bus route and close to some of the cheaper hotels on the edge of the city centre)...