The thermal baths at Locanda di San Martino look lovely. Has anyone used it? If so, around how long did you spend there? Since it has a small capacity, I'm thinking that a reservation would be a good idea.
My husband and I used the thermal baths while we were on this tour. We went down during our free time and spent around an hour, maybe an hour and a half. I know we did not make a reservation and it was not busy. As I recall, there were private stalls to change with lockers to store your things in while enjoying the baths.
Stayed there last June and used the spa twice. The water is not hot but comfortably warm. I think reservations would be wise but it was not crowded when we used it in late afternoon. A great way to relax after walking around Matera all day.
RDJ
I had not previously been a sauna/steam bath person, but after visiting this spa I definitely make use of them at my home gym (and it's a lovely call back to this trip). I was on the 2016 south of italy tour, and I went with several tour mates - I think we ended up staying an hour plus (but we were in a group, chatting and having fun), and we did make reservations - although as someone else said, I don't think it would have been absolutely necessary.
I would definitely say do it!