Tau protein aggregation underlies a spectrum of neurodegenerative disorders collectively known as tauopathies, which manifest through a broad range of clinical symptoms, including motor and behavioral abnormalities, cognitive decline, and age-related memory impairment. Despite decades of research, effective disease-modifying therapies remain elusive. Detailed nanoscale investigations of individual tau aggregates are therefore essential to elucidate the structural heterogeneity that may underlie distinct pathological mechanisms and clinical phenotypes. This review summarizes current knowledge on the structure and morphology of fibrillar tau species at the level of individual filaments. Particular attention is given to the structural diversity of fibrillar tau assemblies, as well as to nanoscale insights into the inhibition of tau assemblies and interactions of tau. The review covers the advances in nanoscale research employing scanning probe microscopy (SPM)-based techniques, including atomic force microscopy (AFM), tip-enhanced Raman spectroscopy (TERS), and infrared nanospectroscopy (AFM-IR). By integrating structural and morphological information at the nanoscale, this review aims to outline emerging directions for understanding the heterogeneity within tau assemblies underlying tau-driven neurodegeneration.