The first spot is generally off the west coast of Gili Meno, where there are some coral, plenty of fish and a drop-off.
The reef here isn't in the best state unless you drift down to behind the break and, as most of the boats seem to go to the same spot, it can get a little congested.
The second is a drift snorkel of about 500m along the east coast of Gili Meno. This is where you are most likely to see turtles, but the coral is banged up and it is a long swim for novice swimmers, with a bit of a current.
The last spot is off the southern tip of Gili Air. This was the highlight with some quite good coral and plenty of aquatic life. If we were to do this again we'd not bother first the first two and just head straight to Gili Air.
The trips generally leave at 10:30 and return at 15:30 and include mask and snorkel but not fins. Lunch is eaten on Gili Air. We were promised, guaranteed in fact, that the boat wouldn't take more than around 20 people. In practice we had 44 passengers, including crew. If you prefer a less crowded trip, there is a more expensive boat that, in theory, limits passenger numbers to no more than 12.
The most commonly sold trip costs 75,000 rupiah per person, including mask and snorkel. The more expensive trip is 120,000 rupiah. Bring sunscreen and water.