Place the watermelon on a stable cutting surface and use a sharp knife to carefully cut off both ends to create flat, stable surfaces.
Stand the watermelon upright and carefully slice off the rind in vertical sections, revealing the bright red flesh underneath. Remove as much rind as possible while preserving the shape.
Using a serrated knife or a large, sharp knife, cut the watermelon into 1.5-inch thick horizontal slices, making them as even as possible to mimic layers of a cake.
Stack the slices to form a tall, cake-like shape. Use a knife to trim the edges if needed to achieve a neat, smooth cylindrical form.
Wrap the assembled watermelon cake in plastic wrap or place it in a covered container and chill in the refrigerator for at least 2 hours, allowing flavors to set and the texture to firm up.
Once chilled, transfer the watermelon cake to a serving platter. Slice into wedges and serve immediately to enjoy the juicy, crisp texture with the vibrant flesh and crunchy rind.
