Rajaportin Sauna is a Tampere institution: a wood-heated public sauna in Pispala that has been operating since the early twentieth century. It is simple, social, and deeply local, which makes it far more interesting than a hotel spa version of Finnish sauna culture.
Bring the right expectations and check opening times and customs before you go. The reward is not luxury but continuity: steam, wood, neighbourhood regulars, and the feeling that you are joining a Tampere ritual rather than watching one from the outside.