An old access shaft to mines near Bath has been discovered under two business premises.
There are miles of mines beneath Bath
Many buildings in the city were built using stone from the Combe Down mines, which are now being stabilised as the mining put homes at risk of collapse.
The Combe Down Garage and Bath Auto Electrics sit on top of the shaft cover, and have sealed off areas of their business as a result.
It is not known how strong the shaft cover is, or when it can be sealed.
A decision on more than £110m of funding necessary to stabilise the mines will be made by the government later in the autumn.
Foam concrete, sand and limestone have already been used to help stabilise some of the 45 acres of tunnels.
The work is keeping access open to parts of archaeological interest, and ensuring a colony of bats is protected.