The Glass Arkel Erker is part of Museum De Bastei, located in Nijmegen. It symbolizes the small observation tower, the Arkel, that was located on top of the defensive wall "Bastei" in the Middle Ages. The original tower was only meant for guards to observe the river side of the city of Nijmegen without becoming visible to others. The architect of today's museum, Van Roosmalen Van Gessel Architecten e.p., decided to introduce about the same concept in the museum. But with a little twist: today's visitors of the Arkel Erker can observe others and also the other way round. Once you step from the museum into the transparent Arkel Erker everybody outside can see you too. The Arkel Erker is a self-supporting glass structure and is completely insulated. The glass panels measure up to 3,2 m x 5,5 m and the glass weighs together approximately 6000 kg. The load-bearing wall panels are made of 121212 PVB-laminated tempered glass (see image for the structural scheme). The structure has been realized by Si-X in close collaboration with the structural glass engineers of ABT. The floors have been calculated with a floor load of 500 kg/m2 on both floors simultaneously. Small hollow core steel members are hidden inside the floor edges to connect the glass elements together and to transfer the lateral loads from wind. The horizontal loads at the 2nd level are taken over by the steel members at the front edge of the wall panel. All vertical loads are taken by the bottom supports, which makes sure the concrete building floor of the museum can deform independent from the glass structure. The Arkel Erker has been subjected to a with an overall load of 3000 kg with water tanks to validate the structural behaviour of the FEA calculation models (see images) and opened on May 19th 2018.