Self-assembly of nano-building blocks has emerged as a key tool to direct the arrangement and the collective properties of nanomaterials. Nevertheless, the lack of control over larger length scales when nanomaterials are processed typically leads to defects which scale with the dimensions of the specimen. This ultimately limits their structural integrity and hence their development beyond microscale materials and devices. Herein, we propose a new, versatile approach to fabricate at low temperatures a nature-inspired composite material based on self-similar, hard, inorganic structures interconnected via soft, organic layers on two hierarchy levels. The final macroscale composite material presents a robust architecture while still maintaining the instrinsic nano-characteristic, functional properties derived from its nano-building blocks. The obtained nanocrystalline magnetite-based material has a high bending strength, significantly improved fracture toughness, high saturation magnetization and a low coercivity while portraying an adjustable, macroscopic shape in the cm-scale. The presented nanocomposite design, therefore, allows to obtain macroscale components with multifunctional properties fostered through nanoscale features and hence enables advancing nanomaterials towards large-scale engineering applications.