This present study reports a novel model for the study on three-dimensional phononic metastructures endued with ultrawide three-dimensional complete bandgaps. The phononic structure is made of a unique material without composite material composition. Based on the principal of mode separation and global and local modal masses participation, the well-engineered structural configurations give extremely wide bandgaps with the gap-to-mid gap ratio of 157.6% and 160.1% for two proposed prototypes that produce the widest three-dimensional bandgaps ever reported. The band structures are explained by a modal analysis and the findings are further corroborated by developing an analytical model based on monoatomic mass-spring chain and further verified with well-established FEM numerical simulations. Thanks to additive manufacturing, the prototypes are developed by using 3D printing technology and low amplitude vibration test is performed to access the real-time vibration mitigation characteristics. An excellent agreement is obtained between analytical, numerical and experimental results. The effects of material damping on transmission response is also taken into consideration that eventually merge the separated bandgaps to form a broadband vibration attenuation zone. The results reported are scale independent and the proposed strategy may pave the way for developing novel meta-devices to control the noise and vibration, and underwater acoustic waves at a wide frequency band in all directions.