Archaeological excavations at Thetford Priory have revealed extensive drainage systems and undercrofts, but no long, secret escape tunnels.

Detailed archaeological investigations, particularly those conducted by the Ministry of Public Building and Works (a predecessor to English Heritage) in the mid-20th century and subsequent surveys, have meticulously mapped the priory's layout. These digs have uncovered well-preserved foundations, numerous burials, and sophisticated medieval infrastructure, including extensive drains and culverts designed for sanitation and water management. They also identified cellars and undercrofts beneath various buildings, such as the frater (refectory) and dorter (dormitory), which served practical purposes like storage or foundations for upper floors. However, these investigations have consistently shown no evidence of the kind of secret, extensive tunnel networks often imagined in popular lore.