Large detectors located in well-shielded deep underground facilities provide various unique opportunities to search for rare processes originating from dark matter interactions, nucleon decay, double beta decays, etc. I participate in the KamLAND collaboration which built the world’s largest liquid scintillator detector with the primary goal of studying neutrino oscillations. In addition, KamLAND may also provide a very clean environment where searches for new physics can be initiated. In the future the KamLAND detector will be used to search for neutrinoless double beta decays by introducing Xenon-136 gas into the sensitive detector volume. If discovered, neutrinoless double beta decay would help to answer questions about both the absolute scale and the origin of neutrino mass.