A modular portable exercise and sauna tent is an apparatus that provides an enclosed phototherapeutic environment for a user. The size and shape of the apparatus is adjustable depending on the position of the user within the apparatus. The apparatus includes a scaffolding, a thermally insulative cover, and at least one heating lamp. The thermally insulative cover further includes a first panel, a second panel, and an overlay panel. The scaffolding defines an area of heat around the user. The thermally insulative cover encloses the defined area. The scaffolding further includes a first base frame, a second base frame, and a plurality of lateral posts, each of which are adjustable in length. The shapes of the first base frame and the second base frame are both adjustable. The apparatus preferably includes a flooring layer that provides comfort and protection for the user against the ground.