The best place to see manta rays in Bali is at Manta Point on the south coast of Nusa Penida. Getting to the dive site take about one hour from Sanur (where we were staying). When we arrived on the site, we immediately saw one manta ray from the boat so we jumped right into the water. We mostly stood still in the water, looking at the rays circling in the water. There were a few other boats with other divers, snorklers and some people seemingly on their first dive (see the picture with one instructor holding two other divers). A real magical moment.
The two other dives the same day were drift dives. You jump in the water, dive to the depth you want to be at and you let yourself go with the flow. The first one was on the north coast of Nusa Penida and the second one north of Nusa Lembongan. It’s a little like being on a bus or a train under water, watching the landscape go by. We didn’t anything “special”, but we saw a lot of nice things: because the current took us at a faster pace than usual, and also because we were making less efforts we could stay longer (both dives longer than 60 mn).