Major plans to redevelop Bath Abbey have been unveiled.
The £18m project aims to create a new choir school, meeting and learning spaces, and a new entrance to the historical building.
The scheme aims to eventually harness energy from the city's spa waters to heat the building.
Most of the work will be carried out underground and will have little impact on the outward appearance of the Abbey, a spokesman said.
The abbey, which dates back to 1499 and was finally completed in 1611, has more than 350,000 visitors every year.
The current building replaced a ruined medieval cathedral which the Normans began building in about 1090.
Rector Edward Mason said: "While the Abbey may superficially appear changeless, it has always adapted to the times.
"Successive generations have made changes because the Abbey is at the heart of city life and it is now time for this generation to create a fresh footprint."
Once initial work is complete, there are plans to rectify "major problems with the floor and lighting within the building".
Planning applications are due to be submitted later in the year.