We have undertaken a survey of the most massive galaxy structures in the early universe at z=2-4, traced by regions of the highest optical depth from IGM Lyα absorption over large scale of 10-30 Mpc. Our cosmological simulations show a strong correlation between the optical depth of intergalactic Ly-alpha absorption and mass overdensities at scales of 10- 40 Mpc. Based on our simulations and MMT observations, we have developed technique to search for the largest IGM Lyα absorption systems. By examining the absorption spectra of ∼60,000 quasar sight-lines in the SDSS-III at z = 2.32 ± 0.04 we have identified the first field that traced by group of IGM Lyα absorbers, which then can be probed in Ly-alpha emission with our custom narrowband filter. The overdense nature of this field is further suggested by a high concentration of quasars at the same redshift. Our KPNO-4m/MOSAIC narrowband imaging and follow-up LBT/MODS spectroscopy have successfully revealed the large-scale galaxy overdensities in this field. Both our simulation and early observational results suggest the largest IGM Ly-alpha absorption systems could be used as a powerful way of tracing most massive galaxy structures in the early universe. In this talk, I will also highlight the great potential of using the ambitious HSC and future PFS survey to conduct the studies of the IGM and most massive large-scale structures.