Ceramics as advanced materials play an important role in science and technology as they are mechanically robust, can withstand immense heat, are chemically inert. Consequently, there is a direct end-user driven need to find ways for efficiently acquiring free-form 3D ceramic structures. Recently, stereo-lithographic 3D printing of hybrid organic-inorganic photo-polymer and subsequent heating was demonstrated to be capable of providing true 3D ceramic and glass structures. Up to now, this was limited to (sub-)millimeter scale and naturally the next step is to acquire functional glass-/ceramic-like 3D structures in micro-/nano-dimensions. In this paper, we explore a possibility to apply ultrafast 3D laser nanolithography followed by heating to acquire ceramic 3D structures down to micro-/nano-dimension. Laser fabrication is employed for the production of initial 3D structures with varying (ranging within hundreds of nm) feature sizes out of hybrid organic-inorganic material SZ2080. Then, a post-fabrication heating at different temperatures up to 1500 °C in an air atmosphere facilitates metal-organic framework decomposition, which results in the glass-ceramic hybrid material. Additionally, annealing procedure densifies the obtained objects providing an extra route for size control. As we show, this can be applied to bulk and free-form objects. We uncover that the geometric downscaling can reach up to 40%, while the aspect ratio of single features, as well as filling ratio of the whole object, remains the same regardless of volume/surface-area ratio. The structures proved to be qualitatively resistant to dry etching, hinting at significantly increased resiliency. Finally, Raman spectrum and X-ray diffraction (XRD) analysis were performed in order to uncover undergoing chemical processes during heat-treatment in order to determine the composition of material obtained. Revealed physical and chemical properties prove the proposed approach paving a route towards 3D opto-structuring of ceramics at the nanoscale for diverse photonic, microfluidic and biomedical applications.