Disclosed are a prefabricated/modular sauna and methods of manufacturing and assembling a prefabricated/modular sauna. For instance, a prefabricated/modular sauna may include: a base frame; a plurality of posts; a plurality of panels; a roof frame; and a roof panel. The base frame and the roof frame include beams and have beam intersections between adjacent beams, each beam intersection is formed of a lap joint and a connector. The panels are secured in post dados of the posts and beam dados of the beams. The posts are secured in notches of base frame beams and roof frame beams. In some cases, the panels include a pre-packaged sauna assembly panel. In some cases, panels and posts are secured against loading forces, lateral forces, or compression forces by (1) interconnected beams and posts in compression or tension, and (2) mechanical connectors (e.g., pins, bolts, screws).