The refurbishment works will see major improvements made to the public areas of the building, to improve the experience of customers.
This includes the creation of a new entrance hall and reception area and a fresh look for the outside of the building which faces onto Parliament Street.
A number of currently unused rooms will also be put back into use, not least to create more changing space for guests.
It also means more of the bath’s amazing architecture and period features will be visible for the first time in many decades.
The refurbishment is scheduled to be completed by the end of July. It was previously overhauled in 2016 when the baths were completely transformed.
Then, changing rooms were upgraded and a steam room was installed. The Spa Rooms were also redecorated and given new carpets and improved lighting.
New furniture and changing cabinets were also introduced.
While the works are underway, bookings will still be accepted, and, shortly, a new website will launch to promote the baths.
Councillor Stanley Lumley, cabinet member with responsibility for the baths, said:
We compete in a competitive market and it’s essential we make sure the facilities we offer, and the experience a visitor receives, is as good as it can be.
This refurbishment will transform more of the public areas of the building and bring back into use several rooms which have been hidden away for many years.
I’d like to thank our regular customers for their patience while the work is carried out.
I can assure them the wait will be worth it.