As you explore Bloodstained Ritual of the Night's map, you'll sooner or later bump into an NPC called Benjamin. He'll find himself trapped in a few locations and it's up to you to get him the proper item he needs to return back home.
However, even finding Benjamin's locations involves a fair bit of running around. Here are all the places he travels to in Bloodstained Ritual of the Night.
Bloodstained Ritual of the Night Benjamin Locations
The first location in which you'll encounter Benjamin is actually in Bloodstained Ritual of the Night's Castle Entrance, in a room that's back to back to one of the Fast Travel rooms in the area (marked green on your map). Giving him a Waystone will fulfill his request for an item, making him teleport away and reward you 1,000 gold.
Afterwards, you'll find him in the Forbidden Underground Waterway. Benjamin's location in this area can be found in the Waterfall room. There's a breakable wall on the right side, around the middle point of the room, and he waits just behind it. You're going to need the Invert ability to reach him and, once you offer him a Waystone he rewards you with 5,000 gold.
The last location you'll find Benjamin in is the room with two red bridges found in Bloodstained Ritual of the Night's Oriental Sorcery Lab area. He waits under the stone archway and you're going to need the Dimension Shift ability to get to him. Simply give him another Waystone and he'll teleport away while rewarding you with 10,000 gold.
After finding Benjamin in all three locations, speak with him back in Arvantville where he'll give you the final reward: the Adversity Ring. This also brings his quest to its end. Equipping the ring increases your power while status afflicted.