Entering the deepest tombs of the "forgotten" pyramids of Nuri would be a challenge even for Lara Croft. Hidden among 20-odd ancient pyramids, like grand termite mounds sticking up out of the Nubian sands of northern Sudan, is a stony 65-step stairway that leads to a murky pool of water. Once you're up to your shoulders in water, the only way to the burial chamber is to take a plunge and swim through a series of submerged inner chambers.

But this wasn't enough to stop the Nuri Archaeological Expedition. As reported by National Geographic this week, a team of marine archaeologists recently ventured into a submerged tomb at the ancient royal burial site of Nuri, becoming the first people to set eyes on the pharoh’s tomb for at least a century. Their work was supported by the National Geographic Society.

©Nuri Archaeological Expedition/Abagail Breidenstein

The Royal Pyramids and the Nuri Royal Cemetery are found in northern modern Sudan, along the west side of the Nile. As many as 80 pyramids were built between 650 BCE and 300 BCE, although only 20 or so now remain. The pyramids are the final resting place of up to 60 Kushite kings and queens, the so-called “black pharaohs” of the Nubian kingdom who vied for power against their Egyptian neighbors. One of the oldest pyramids was built as a tomb for Taharqa, the fourth king of the 25th dynasty of ancient Egypt who reigned until 664 BCE, who fled to Nubia after he lost power.

The burial chamber has not always been flooded with water, although it has proven to be an excellent guard against grave robbers over the past 100 years. The tombs have only become submerged in recent decades due to groundwater from the nearby Nile that has been rising due to climate change, agricultural intensification, and a newly constructed dam along the Nile.

©Nuri Archaeological Expedition/Pearce Paul Creasman

To gain access to the submerged inner chambers, the excavation team had to dive through the water with hoses that pumped oxygen from the surface. This is thought to be the first time underwater archaeology has been carried out in Sudan.

"There are three chambers, with these beautiful arched ceilings, about the size of a small bus, you go in one chamber into the next, it's pitch black, you know you're in a tomb if your flashlights aren't on. And it starts revealing the secrets that are held within," Pearce Paul Creasman, marine archaeologist and Egyptologist, told BBC Newsday.

©Nuri Archaeological Expedition/Arthur Piccinati

One of the tombs that was recently explored by the Nuri Archaeological Expedition is thought to have belonged to Nastasen, a pharaoh who ruled the Kush kingdom from 335 BCE to 315 BCE. Within these chambers, archaeologists discovered several gold flakes that once covered small statues and figurines.