The Herschel space mission has generated, for the first time, a rich data set that allow us to explore the far-IR (FIR) universe at z > 1 on a large scale that is comparable to those in optical/near-IR. As the mission is now over, these are the best -- and all -- that we can have before the next generation FIR facilities arrive. We are undertaking a program to study the extreme, dust-enshrouded star formation in galaxies at z >1, targeting the Ultra-Luminous InfraRed Galaxies (ULIRGs) revealed by the Herschel very wide-field surveys. The most serious challenge is the persisting problem of poor angular resolution in FIR/sub-mm that the Herschel still suffered. We are developing a method to extract the major component(s) of Herschel sources using optical data directly as the position priors, which is appropriate to the study of ULIRGs. We will construct the largest, well-defined sample of high-z ULIRG, whose total IR luminosity are directly measured based on multiple FIR bands, and to enable a slew of follow-up studies. Some preliminary results will be presented here.