Nusa penida is famous for snorkeling with manta rays. We snorkelled with them for sunrise and had them all to ourselves. This activity needs a good level of fitness and you shouldn't be afraid of big waves and the ocean. We texted +62 819 3697 6234 and they will sort any request out for me. They will organize the snorkeling with the manta rays. Here is their website: https://baliomtours.com/