The Castle Street Culvert is often mistaken as a ‘smugglers‘ tunnel, although it is no such thing.
Down the middle of Castle Street runs a stone culvert. This was discovered during excavations in 2008. Off of the main culvert run smaller culverts at right angles, which connected it to the cellars of the houses of Castle Street. Although the sides of the structure were stone, the roof was of brick construction, suggesting that that part at least dates to the early eighteenth century and the construction of Castle Street.
The culvert was probably an early sewerage system, conveying waste out to the river. It may have been completely built in one phase during the building of Castle Street, although the stone section may show eighteenth century reuse of an earlier structure, perhaps associated with Harvey’s grand house that once stood at the top of the street. [1]
[1] Place, C., ‘Castle Street, Bridgwater, Somerset’ (2009) in the Somerset Historic Environment Record p.23
For more on the supposed tunnels below Bridgwater, see this video: