Soften the wood of the stump. Wait for a day after a rainstorm when the wood will be softer and more pliable after absorbing water. This is not necessary, but will make the job easier.
Drill holes across the section of the stump you wish to make hollow. Space the holes a few inches apart throughout the entire section.
Hollow out the stump with your hammer and chisel. Chip away the wood beginning at the edge of one of the holes. Keep your chisel at a 45-degree angle. Remove the wood and place it in a compost pile, recycle pile or use it as mulch.
Smooth the hollowed area. Clean up the hollow by chiseling away the jagged sections of wood. Smooth the edges and bottom of the hollow with course-grain sandpaper.
Wipe away any debris or dust from your work.