Apparatus comprising the following: - a frame structure; and - a first surface element and a second surface element; wherein the first surface element and the second surface element are guided horizontally slideable along the frame structure, wherein the first surface element has approximately twice the width of the second surface element, wherein the first surface element has a vertical center axis, on which it is fastened on its top side horizontally centered on the rotating part of a top carriage and on which it is fastened on its bottom side horizontally centered on the rotating part of a bottom carriage, wherein the top and the bottom carriage (30, 40) act as a horizontal guide for the first surface element, wherein the first surface element is swivably fastened on one of its vertically oriented lateral end sides on a vertically oriented first lateral end side of the second surface element, and wherein the second surface element, on a vertically oriented second lateral end side, is arranged on a vertically oriented part of the frame structure such that the second surface element is fastened on the frame structure swivably about a vertical longitudinal swivel axis, characterized in that the bottom carriage comprises eight bearing rollers (31a, 32a; 31b, 32b; 31c, 32c; 31d, 32d), wherein the bearing rollers (31a, 32a; 31b, 32b; 31c, 32c; 31d, 32d), which share a common axis in pairs, rest on a bottom part of the frame structure on a guide rail arranged thereon such that their respective wheel flanges provide a good guide transversally to the direction of travel, whereas their respective rolling surfaces have a sufficiently wide design to ensure a low-wear, easy rolling motion in the direction of travel. - a frame structure; and - a first surface element and a second surface element; wherein the first surface element and the second surface element are guided horizontally slideable along the frame structure, wherein the first surface element has approximately twice the width of the second surface element, wherein the first surface element has a vertical center axis, on which it is fastened on its top side horizontally centered on the rotating part of a top carriage and on which it is fastened on its bottom side horizontally centered on the rotating part of a bottom carriage, wherein the top and the bottom carriage (30, 40) act as a horizontal guide for the first surface element, wherein the first surface element is swivably fastened on one of its vertically oriented lateral end sides on a vertically oriented first lateral end side of the second surface element, and wherein the second surface element, on a vertically oriented second lateral end side, is arranged on a vertically oriented part of the frame structure such that the second surface element is fastened on the frame structure swivably about a vertical longitudinal swivel axis, characterized in that the bottom carriage comprises eight bearing rollers (31a, 32a; 31b, 32b; 31c, 32c; 31d, 32d), wherein the bearing rollers (31a, 32a; 31b, 32b; 31c, 32c; 31d, 32d), which share a common axis in pairs, rest on a bottom part of the frame structure on a guide rail arranged thereon such that their respective wheel flanges provide a good guide transversally to the direction of travel, whereas their respective rolling surfaces have a sufficiently wide design to ensure a low-wear, easy rolling motion in the direction of travel.