The project IMAGINE_IT (PI Dr. Dimitri Komatitsch) received 40 million CPU-hours on the Tier-0 GENCI/TGCC CURIE supercomputer as a winner of the 9th PRACE consortium call (2014). The awarded computational resources allowed us to construct a new 3D tomographic model for the Italian lithosphere, Im25, by combining spectral-element three-dimensional wavefield simulations and an adjoint-state method. To obtain the final model Im25, we performed 25 adjoint tomography iterations and two source inversion iterations for the initial wavespeed model and an intermediate one. The 3D model Im25 resolves P- and S-wavespeed values in the Italian lithosphere for frequencies up to ~0.1 Hz (i.e., periods down to ~10 s). It provides improved images of the subsurface of the peninsula and its neighborhood, highlighting the complex structure of the Adriatic plate on the east of the Italian coast, the debated plumbing system of Mount Etna volcano, and the distribution of fluids and gas (CO2) in correlation with the Italian seismicity. The obtained Vp and Vs models are in agreement with high resolution models developed by classical tomography studies in Italy at local scale, and the retrieved Vp/Vs values correspond to the interpretations on fluids and gas distribution in the Italian subsurface from studies in various geophysical fields. The Vs Im25 model also compares favorably with Vs profiles extracted from other studies that use different techniques and datasets, and focus on specific zones of Italy. The provided dataset contains the values of Vp and Vs (in m/s) for model Im25 at each point of the geometrical grid used to discretize the study volume.