We report the synthesis of various iron oxide nanocontainers and Pt-iron oxide nanoparticles based on a cast-mold approach, starting from nanoparticles having a metal core (either Au or AuPt) and an iron oxide shell. Upon annealing, the particles evolve to asymmetric core-shells and then to heterodimers. If iodine is used to leach Au out of these structures, asymmetric core-shells evolve into "nanocontainers", that is, iron oxide nanoparticles enclosing a cavity accessible through nanometer-sized pores, while heterodimers evolve into particles with a concave region. When starting from a metal domain made of AuPt, selective leaching of the Au atoms yields the same iron oxide nanoparticle morphologies but now encasing Pt domains (in their concave region or in their cavity). We found that the concave nanoparticles are capable of destabilizing Au nanocrystals of sizes matching that of the concave region. In addition, for the nanocontainers, we propose two different applications: (i) we demonstrate loading of the cavity region of the nanocontainers with the antitumoral drug cis-platin; and (ii) we show that nanocontainers encasing Pt domains can act as recoverable photocatalysts for the reduction of a model dye.