Environmental enrichment is a model of increased structural brain plasticity. Previous histological observations have shown molecular and cellular changes in a few pre-determined areas of the rodent brain. However, little is known about the time course of enrichment-induced brain changes and how they distribute across the whole brain. Here we expose adult mice to three weeks of environmental enrichment using a novel re-configurable maze design. In-vivo MRI shows volumetric brain changes in brain areas related to spatial memory, navigation, and sensorimotor experience, such as the hippocampal formation and the sensorimotor cortex. Evidence from a second cohort of mice indicates that these plastic changes might occur as early as 24 h after exposure. This suggests that novel experiences are powerful modulators of plasticity even in the adult brain. Understanding and harnessing the underlying molecular mechanisms could advance future treatments of neurological disease.