We present a continuum theory of frustration-limited clusters in one-component glass-forming liquids that accounts, in part, for the recently reported [Fischer et al., J. Non-Cryst. Solids, 131-133, 134 (1991)], and quite unexpected, presence in simple glass-forming liquids of stable clusters at low temperatures (T) and the even less expected persistence for very long times of these clusters at higher Ts. The model is based on the idea that there is B local structure that is energetically preferred over simple crystalline packing, which is strained (frustrated) over large distances; although in a curved space the preferred packing could lead to "ideal" crystallization at temperatures that are usually above the actual freezing temperature, in "flat" space this transition is narrowly avoided. We are led to a new ansatz for the T dependence of the viscosity, which permits us to collapse data for many liquids onto a universal curve.