La Altagracia, Dominican Republic
Hoyo Azul is a very big sinkhole and popular local hangout, on weekends people will be cooking, swimming and generally getting drunk and disorderly.
To get there go straight about 2-3 K past the Cueva de Berna turn off park at the first curve in the road.
You need to hike about 15 mins and climb up to get to the top of the sink. From here it will take about five minutes to climb back down and the rocks are very slippery. Be especially careful of wasp nests when climbing down the sink, they are hard to see so take your time and check your surroundings, if you get within a few feet you will be viciously attacked, and DR wasps are no joke. The sink entrance pool is not huge but underwater it is a massive cavern, roughly the size of a large supermarket, there is a very pronounced halocline at only 5 meters and at 15 there is a hydrogen sulfide layer that is totally opaque. Immediately to the right in the ceiling at 5 meters, there is a section that looks like Swiss cheese with tunnels branching off in all directions, this area will silt out and percolate fiercely so be prepared, it is through this section that Hoyo Azul connects to El Toro 2, a very cool traverse.
On this line after passing a very tight restriction there is a massive room, that goes from 4 to 30 meters straight down, an underwater sinkhole of sorts and worth the dive alone.
From the cavern as you go down along the wall and pass through the hydrogen sulfide layer, and get to the bottom there is a horizontal fissure that leads to a huge cylindrical room, here the rock is coated with a super fine layer of white silt that looks like snow and the room bottoms out at 30 meters.
Hoyo Azul is a sidemount dive, although the cavern area is massive, the connection to El Toro 2 and all the bedding planes are very low.
Extreme silt outs are the norm here too due to fierce percolation. This is an advanced side mount dive. expect zero viz exits on every dive.