Geometrically frustrated spin systems have been studied extensively for decades because of many intriguing phenomena, exemplified by the non-magnetic quantum disordered states. On the other hand, there is a long history of studying interactions between the localized and conduction electrons in Ce or Yb compounds, which typically results in the Kondo-lattice or valence-fluctuation states. A combination of such Kondo-lattice state and geometrical frustration becomes a new topic, both enhancing quantum fluctuations in different routes. In this proposal, we would like to investigate CeRhSn, which is recently found to be a model compound belonging to this new class. We would like to elucidate the origin of quantum critical behavior detected in the bulk measurements by investigating its low-energy spin fluctuations in detail.