Sand your piece of wood until it is smooth and splinter-free. Round off the edges for a nicer look, if preferred.
Measure and mark the center of each hole, keeping the markings at least 4 inches away from each other. This will give you about 2 1/2 inches between holes in the final product, ensuring that the wood won't crack under your weight.
Drill your holes with a 1.5-inch drill bit, making them as straight as possible. If you angle them, your board may be nearly impossible to climb.
Sand the edges of the holes to avoid splinters. Do not sand too much, or the holes will be too big.
Measure the width of your hand and add 4 inches. Cut your dowels to this length.
Test the dowels in the holes. Sand the ends of the dowels until they fit all the way into the holes. They should fit snugly but still be easy to remove.
Varnish your board and dowels following the directions on the can. This is optional but will make your board more durable. Once the varnish has dried, make sure the dowels still fit in the holes and sand them down if necessary.