The blue-green, brackish water at the bottom of this peculiar 40m-by-20m limestone hole invites a swim and a snorkel. The intrepid can inch round the ledges that surround the pool and dive into the deep unknown. The sinkhole, the depth of which is still uncertain, is known locally as Bayt Al Afreet (House of the Demon). If the demon eludes you, look out for the equally elusive blind cavefish instead. The site is surrounded by a pleasant park.
The sinkhole is beside the Muscat–Sur portion of Coastal Hwy 17, near the village of Dibab. Follow the signposts for Hawiyat Najm Park towards a green oasis. There are toilets but no changing or other facilities at this shady and popular picnic spot.
From the sinkhole you can drive along the old coast road (which runs beside the shoreline) for a closer look at the sea, and rejoin the highway at the next junction in either direction.