A visual study was conducted on the boiling behavior, especially the dry-out and rewetting process, in a three-dimensional porous structure made of staggered glass beads. The bead-packed structure was filled with water, and heated from below. Using a high-speed video imaging system, pore-scale bubble growth behavior in the bead-packed structure was observed. In the pore-scale view, it was found that the narrow-gap corner between a glass bead and the heated wall is a dual-effect area that is a very active wetting area as well as an active bubble-generation area. Replenishment that plays a very important role on the dry-out and rewetting process is a unique characteristic in the bead-packed structure, and also the liquid supply for wetting effect of the narrow-gap corner zone.