As longtime readers of the Sebastian St. Cyr series know, Jamie Knox's tavern, the Black Devil, backs onto the churchyard of St. Helen's, Bishopsgate.
St. Helen's still exists today, having come through both the Great Fire and the Blitz. In fact, it is the largest surviving church in the City of London. Built in the 13th century as part of a priory of Benedictine nuns, it contains twin naves once separated by a wall (the northern nave was for the nuns, with the adjoining nave for parishioners). After the Dissolution, the central wall was torn down and the other priory buildings repurposed rather than destroyed. It wasn't until 1799 that most of the other old monastic buildings disappeared.
Unfortunately, the church was badly damaged by IRA bombs in the 1990, when many of its famous interior monuments were lost and its huge medieval stained glass window shattered. It has since been repaired, but you can compare the above image of the interior with an old photograph, below.