Dig a 24-inch-deep post hole with a shovel or post hole digger. Pour 6 inches of gravel into the hole and tamp firmly.
Fill the post hole with water. Allow the water to soak into the soil.
Place the 4-by-4 post into the hole. Pour a bag of quick-setting concrete into the hole around the post. Adjust the post, using a spirit level to ensure that it is vertical. Add water to the concrete mix in the hole. Allow the concrete to dry overnight.
Apply construction glue to the top of the post. Set the post cap in place and press down firmly.
Drill a hole straight down through the center of the post cap and into the post. Apply construction glue to the bottom of the finial and then screw it into the top of the post.
Mark the center on each side of the post, just under the post cap. Mark and cut the tops of four 2-by-2 boards at a 60-degree angle. Use a miter box and saw to make the cuts.
Center the first 2-by-2 on one side of the post, butting the angled edge up to the post cap. Drill two pilot holes through the board and into the post. Attach the board to the post with construction glue and deck screws. Repeat on the other three sides of the post.
Mark the angled boards at 1, 3 and 5 feet from the ground. Measure the distance between the marks. Cut the remaining 2-by-2 boards at a 45-degree angle to fit horizontally between each set of marks.
Drill pilot holes at an angle through each horizontal board and into the tall angled boards. Apply construction glue and then screw the boards together to complete the pyramidal shape of the obelisk.
Plant a flowering vine next to the post.