An attachment device for securing a shelter to a rigid structure, the shelter comprising a flexible panel, and the attachment device comprising: - an anchor element for securing to a substantially vertical surface of the rigid structure, the anchor element comprising a suction disc and a threaded post, the suction disc comprising on opposite sides a first surface and a second surface, the first surface being configured to create a partial vacuum between the anchor element and said surface whereby, in use, the anchor element is secured to said surface and the threaded post extends away from the second surface whereby said post extends in a direction away from the surface of the structure when the anchor element is secured to the structure; - a clamping element including a threaded recess or bore for receiving and engaging with the threaded post to secure the clamping element to the anchor element, such that a part of said flexible panel is clamped between the anchor element and the clamping element; and - a grip element located between at least a part of the anchor element and the clamping element, the threaded post extending through an aperture in the grip element wherein the grip element is shaped and configured to allow a central region of the first surface of the suction disc to be pulled in a direction away from said substantially vertical surface of the structure to create the partial vacuum while an edge region of the first surface remains in contact with said surface of the structure; and characterised in that: the grip element comprises a flange configured such that, in use, the flexible panel is clamped between the flange and a part of the anchor element. - an anchor element for securing to a substantially vertical surface of the rigid structure, the anchor element comprising a suction disc and a threaded post, the suction disc comprising on opposite sides a first surface and a second surface, the first surface being configured to create a partial vacuum between the anchor element and said surface whereby, in use, the anchor element is secured to said surface and the threaded post extends away from the second surface whereby said post extends in a direction away from the surface of the structure when the anchor element is secured to the structure; - a clamping element including a threaded recess or bore for receiving and engaging with the threaded post to secure the clamping element to the anchor element, such that a part of said flexible panel is clamped between the anchor element and the clamping element; and - a grip element located between at least a part of the anchor element and the clamping element, the threaded post extending through an aperture in the grip element wherein the grip element is shaped and configured to allow a central region of the first surface of the suction disc to be pulled in a direction away from said substantially vertical surface of the structure to create the partial vacuum while an edge region of the first surface remains in contact with said surface of the structure; and characterised in that: the grip element comprises a flange configured such that, in use, the flexible panel is clamped between the flange and a part of the anchor element.