Would love to avail of the whole turkish bath/ steam room / sauna thing on the same basis, but so far have not found such a pay-as-you-go facility in town.
Closest I've come is the YMCA on Aungier Street, where there is (quite a decent) sauna in the ladies and gents changing rooms, along with an adjacent cold shower tap. It's basic but does the job nicely and the fact its in the changing room makes it quite easy to use.
The only other place I've been to outside of a club or fitness centre was the Markievicz Leisure Centre in Townsend Street, which has a largish sauna installed beside the pool. In theory its great but in practice its not fantastic because the heat in the sauna could be higher and the door is constantly opening and closing with swimmers coming in and out. Have sat there and been only okay warm with cold feet! There is no facility to put water on the coals or generate any steam.
In the evening, it can also get rather crowded with people even standing waiting for a seat. The cold shower tap is in the changing rooms which are a bit of a walk from the sauna itself or you go into the pool. Just not really set up for a proper sauna IMO.
If anyone else knows of anyplace in town which is set up for a proper heat/cold sauna session, please post the details!