This study aims to use architectural sandstone balusters with a concave-convex geometry to investigate the potential influencing factors during softening/destruction due to fire loading. The thermo-mechanical behaviour of large-size sandstone balusters under real fire conditions was investigated via laboratory tests and numerical simulations. It was found that the spalling of sandstone balusters undergoing extreme temperature regimes is mainly due to the coalescence of tensile cracks formed inside the sample during heating and those formed in the outer layer of the sample during cooling. Both simulation and lab test results show that the object shape significantly influences thermal-induced stresses and cracks. Compared to the impact of the selected baluster shape, the influence of heterogeneity is relatively small. However, the temperature distribution has a dominant impact on the fracturing behaviour of the sandstone samples. These findings are the basis for discussing the fire-induced damage evolution in architectural sandstone elements.