Blackfriars (Gloucester)

English Heritage
Remains of a Dominican friary, sited in the centre of Gloucester, and finished about 1270. After the dissolution of the monasteries, the church was shortened and converted into a Tudor mansion, and the outbuildings into a cloth factory. Later additions have been stripped away so that the medieval fabric is again visible. The site is managed by Gloucester Council who use the church for events.
The church interior is well worth a look, with its surviving stonework and arches, and the interesting roof. Also see the upstairs of the building (south range) on the other side of the courtyard, which is regarded as the oldest surviving purpose built library in the country. It has original roof beams and niches where the monks worked. Note the scissor-brace roofs.
Before travelling, check the EH website for the restricted opening times. Access October-March seems to be by appointment only.
With luck, using a satnav + postcode will take you to a car park outside the friary.