St John's Church stands just south of the castle mound and is the older and more interesting of Devizes's two medieval churches. The exterior is dominated by its Norman crossing tower, built around 1130 and barely altered since. Go inside for the chancel arch, which is a masterpiece of Romanesque carving — the zigzag chevrons and grimacing beak-head figures are in remarkably good condition after nine centuries.
The church is usually open during the day and entry is free. It is quieter and less well-known than the Wiltshire Museum, but for anyone interested in Norman architecture it is essential. The churchyard is pleasant and gives a good view up to the castle. A brass plaque inside commemorates some of Devizes's worthies going back to the medieval period. Allow 30-45 minutes, more if you want to read the monuments carefully.