Mokuola, often called Coconut Island, is a small island park in Hilo Bay connected to shore by a footbridge. It is not a grand attraction, but it is one of the easiest places in Hilo to sit by the water and look back at the bayfront and Mauna Kea when the clouds allow.
The island also carries Hawaiian cultural associations, which give the casual park setting more depth. Go for a short wander, a picnic, or a pause after Liliuokalani Gardens rather than expecting a full beach day.