Nothing remains of Christina's monastic foundation in Markyate in Hertfordshire (except, a local friend tells me, for a subterranean tunnel linking her priory to an abbey nearby). So instead, we filmed the opening sequence of the module at Lilleshall Abbey in Shropshire.
The final sequence was filmed at Lacock Abbey in Wiltshire, in same cloister that features in many of the Harry Potter films.
Lacock is well worth a visit. It really retains the feel of a 15th century convent. And the local town - administered by the National Trust - is a gem.