Enormous Ly$alpha$ nebulae (ELANe) represent the extrema of Ly$alpha$ nebulosities. They have detected extents of $>200$ kpc in Ly$alpha$ and Ly$alpha$ luminosities $>10^{44}$ erg s$^{-1}$. The ELAN population is an ideal laboratory to study the interactions between galaxies and the intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes. The current sample size of ELANe is still very small, and the few $zapprox2$ ELANe discovered to date are all associated with local overdensities of active galactic nuclei (AGNs). Inspired by these results, we have initiated a survey of ELANe associated with QSO pairs using the Palomar and Keck Cosmic Web Imagers (PCWI/KCWI). In this letter, we present our first result: the discovery of ELAN0101+0201 associated with a QSO pair at $z=2.45$. Our PCWI discovery data shows that, above a 2-$sigma$ surface brightness of $1.2times10^{-17}$ sbunit, the end-to-end size of ELAN0101+0201 is $gtrsim 232$ kpc. We have conducted follow-up observations using KCWI, resolving multiple Ly$alpha$ emitting sources within the rectangular field-of-view of $approx 130times165$ projected kpc$^2$, and obtaining their emission line profiles at high signal-to-noise ratios. Combining both KCWI and PCWI, our observations confirm that ELAN0101+0201 resides in an extremely overdense environment. Our observations further support that a large amount of cool ($Tsim10^4$K) gas could exist in massive halos (M$gtrsim10^{13}$M$_odot$) at $zapprox2$. Future observations on a larger sample of similar systems will provide statistics of how cool gas is distributed in massive overdensities at high-redshift and strongly constrain the evolution of the intracluster medium (ICM).
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