Reef mantas visit cleaning stations off Nusa Penida's south-west coast most of the year. On your own boat you reach them when the skipper judges the sea is right, not when a group schedule says so, and you have a guide in the water beside you.
Manta Point lies under the cliffs, open to the Indian Ocean. The mantas circle a few metres below the surface while small fish clean them, and on a good day several pass beneath you at once. Sightings are very likely through most of the year but never certain.
After the mantas, two calmer reefs: Crystal Bay or Gamat Bay for coral and reef fish, then a sheltered site where turtles are often seen. Lunch is at a beach club on Nusa Lembongan before the run home.
Stay at least three metres away, never touch them, and don't chase or dive down onto them. A manta's skin is protected by a coating that a touch strips away. Your guide will brief you on the boat.