The invention relates to an expandable, mobile accommodation of activities comprising a central structure which is provided with floor (10) and roof (3) and front and rear end walls (1, 2) and two longitudinal side walls (8, 9). Two side walls (4, 5; 6, 7) are arranged outermost on each side of the central structure capable of being turned outwardly perpendicular to the central structure. Guide rails (15, 16) are attached to the inside of said side walls for guiding of the longitudinal side walls (8, 9), which are movable outwards in parallel motion, and of the mutually hinged roof and floor sections (12, 11), the outermost sections of which being hinged to the outwardly movable side walls (8, 9), and the innermost sections of which being hinged to the roof (3) and floor (10), respectively, of the central structure. Said roof (3) is journalled movable in vertical direction guided in vertical guide rails (17), and in non-expanded state the roof sections (12) are positioned lying like a package on one of its sides on the roof (3) of the Central structure, which roof is in its lowered position. At starting of the expanding the package of roof sections is tilted up in upright position during movement of the roof (3) of the central structure upwards, and movement of the outwardly movable side walls (8, 9) outwards, which latter movement is arranged to continue until said side walls (8, 9) and roof and floor sections are in their end positions, preferably with pair of roof sections forming ridges. In order to achieve an extended ceiling height, the movable side walls (6, 7, 9) are, according to the invention, provided within non-expanded state inwardly folded sections, which in expanded state are raised for extended height, in addition to which hydraulic cylinders (60) are arranged to impart to the roof (3) of the central structure the required increase of the lifting height corresponding to the increased height of the side walls.