Probing the thermodynamics of polymer confinement in small pores, single DNA molecules were imaged by fluorescence microscopy as they partitioned within a pair of adjacent interconnected spherical cavities prepared by the colloidal templating method. This method produces. pores of precisely known geometry and controlled level of confinement. As expected.. a polymer weakly or moderately confined by cavities of unequal diameter was observed to maximize its configurational entropy by partitioning toward the larger cavity. The polymer's cavity-to-cavity partition coefficient could be derived from -the visualized bias in cavity occupation, and segmental excluded volume notably influences how this coefficient depends on chain length and two cavity sizes. A DNA molecule strongly confined within a pair of equalsized cavities predominately adopts "bridging" configurations, splitting its segments between the two cavities. Segmental excluded-volume stabilizes such configurations; the stability, reveak that a chain must overcome a doubly peaked energy barrier to move between cavities.