Not sure what it's like but I've heard good things. Going over on the train from Bristol next week for a 4 hour session for the price of 2. That's £24 instead of the normal £34 for a 4 hour session:
There is no better way to travel to Bath Spa than by train and use the good services of First Great Western. Now you can take advantage of a special offer which entitles rail users to enjoy a 4-hour spa session for the price of a 2-hour spa session at Thermae Bath Spa. The main railway station in Bath is an easy 10-minute walk from the Spa.
There is no need to collect tokens or coupons, simply download a voucher under the '2for1 offers in Bath, Bristol and Oxford' from http://www.firstgreatwestern.co.uk
or go directly to:http://www.firstgreatwestern.co.uk/Content.aspx?id=3024#15%20Thermae%20Bath%20Spa.
The offer is valid Monday - Friday until 31 May 2010 (not Saturdays and Sundays)during the normal opening times of 9.00 - 22.00. To gain full use of the 4-hour spa session, last entry is at 17.30. There is no need to book the spa session in advance. Guests need to bring their own swimming costume. If required, towel, robe and slippers can be hired from the Spa. No entry for children under 16.