Abstract The origin of the thermal springs of Bath (England) remains unknown. As part of a programme of research into the structure of the thermal aquifer, the Carboniferous Limestone, an urban reflection seismic survey has been carried out to explore the deep geology of the Bath area. Existing gravity data have been used to provisionally identify the seismic reflectors and to map the depth of the (interpreted) Carboniferous Limestone in the area around the springs. The new seismic data show that at a distance of 2.1 km south-west of the springs, the depth of the (interpreted) Carboniferous Limestone surface increases from 0.4 km below Ordnance Datum (OD) to 1.35 km below OD within a distance of 1.8 km, an average apparent dip of nearly 30 degrees. In all other directions from the springs, the Carboniferous Limestone surface is at a depth of 300 m or less below OD. The work described in this paper is part of a continuing research programme.