Located just to the east of the Bali to Java ferry terminal near the town of Gilimanuk is Secret Bay.
Teluk Gilimanuk is about two kilometers across and very shallow, less than 10 meters deep with an average of 4 to 5 meters. There are two small islands inside of the bay, Pulau Kalong and Pulau Burung, they are actually barely more than sandbars. The bay and it's surrounding mangrove areas are a nursing ground for fish as the water is fed by upwellings brought by the daily tidal changes from the cool, plankton rich Bali Strait.
Secret Bay is one of the best muck diving sites in the world, there are no coral reefs, just a unique plateau of black volcanic sand teeming with macro critters.
The best time to dive is on the incoming tide or around high tide, it doesn't matter if it's early or late in the day, as the bay will have filled with clear water from the Bali Strait. The water temperature is slightly cooler here at about 23-25 degress. There is a fair bit of debris around which forms myriad hiding places for countless creatures including dragonets, seahorses, ghost pipefish, nudibranchs, red and white segmented sea cucumbers, gobies, frogfish, scorpionfish, hermit crabs and octopus. There have even been sightings of 4 meter Bobbitt worms in the bay, these creatures live in burrows and are armed with fangs and lightning speed with which they dispatch their prey. This dive site truly is a macro photographers paradise.