Sacred Falls, Oahu
Sacred Falls, which is named after the 1,370-acre state park that it resides in, is a beautiful waterfall on Oahu that is surrounded by rocky cliffs and greenery. It drops 80 feet (24 m) down into a pool. This waterfall used to be one of the most popular ones on the island when it was still accessible via a hiking trail.
However, on Mother's Day of 1999, the trail was closed indefinitely after eight people were killed and 50 others were injured when boulders and rocks collapsed into the narrow Sacred Falls valley where the visitors were unable to escape from the falling debris.
Even before the incident, the area was known to be dangerous because the footing on the park's trail could become very slippery, and deaths had occurred on the waterfall trail when water from flash floods in the mountains swept hikers down the canyon.
The park still remains closed to the public, though there has been advocacy to reopen it with restrictions. For now, the only way you can see the falls is by air, such as while on an Oahu helicopter tour.