On the islands, you can also find NPC merchants from whom you can buy fruits and other weapons (he will have a green question mark above his head). In order to get to another island, you need to find a pier, talk to the NPC and order a free boat. Standing on it you can sail a...
If you want another location apart from Haunted Castle, you can also try out Bone-farming at the Haunted Shipwreck Sea Event since enemies can also drop Bones there. For the Haunted Shipwreck event to spawn for you, you will need to sail a Boat in Sea Danger Level 6. ...