Josh Gates reports on amazing finds at the Indiana Jones site.

Josh Gates has taken viewers everywhere from a lost city in the remote jungles of Cambodia to diving the Caribbean waters in search of sunken treasure. Now the adventurer's goal is to help unseal a long-buried grave containing remains of ancient skeletons. The historic discovery beneath the famous financial building in Petra, Jordan, will be documented as part of the new season of Gates' film. Expedition unknown.

It was 2,000 years ago when the Nabataean kingdom hand-carved an entire city into the walls of a desert canyon and built the magnificent structure known as “The Treasury” in the center. Made famous by housing the Holy Grail, as seen in Indiana Jones and the Last CrusadeThe Treasury's true purpose remains a mystery.

This search for answers was part of a joint Jordanian-American project led by American Center of Research (ACOR) Executive Director and Professor Pearce Paul Creasman. His team received extremely rare permission to conduct a remote sensing scan and dig beneath the Treasury. They made a stunning discovery: a tomb full of at least a dozen Nabataean tombs directly beneath the building, which is visited by more than a million visitors each year.

Ahead of the two-part season premiere, Gates takes us through the groundbreaking dig and what's to come.

Expedition Unknown host Josh Gates at the entrance to Petra. (Photo credit: Discovery)

What plays a role when choosing a travel destination?

Josh Gates: We always want to go to places in the world where active investigations are taking place. We have a network of archaeologists and producers around the world who are always willing to listen to places where active excavation is taking place. Not only do we want to get our viewers to investigate a mystery or legend, but we also want to get our own hands dirty to see what we can find to advance that story. We worked with Petra a few years ago in Sudan with the senior archaeologist there, Pearce Paul Creasman. He dug up a flooded pyramid there. However, his main job is as executive director and professor of ACOR. He said: “Look, we are going to have this really exciting season in Petra and you should definitely come and join us. I think it's going to be special.” When we heard that, we were there straight away.

Talk about some of the physical demands that this particular exploration entailed.

As we often say: It's never easy. Archeology is difficult. Exploration can be a real challenge. In this case, we used a lot of really incredible 21st century technology. Things like GPR or ground penetrating radar to scan in front of the Ministry of Finance, the most famous building in Petra. This is the building that everyone knows as it housed the Holy Grail Indiana Jones and the Last Crusade. This remarkable technology allows us to perform non-invasive scans in front of this building, one of the new Seven Wonders of the World. It is a world heritage site visited by a million people every year. In a place like this you have to be careful, but as soon as technology reveals something, as it did under the Treasury, you have to go physical.

They move tons and tons of earth and seven buckets of this earth to see if there is anything valuable in it in the sense of material culture. I also traveled far beyond the deserts of Jordan to try to understand the world of Petra and the Nabataean people who built it. We drove to very remote places like Sela, a desert fortress where the Nabataeans were at their full potential. To do this, we dangled from a cliff and tried to scan this ancient inscription that had been left there thousands of years ago. The act of exploration is not easy. That's why many of these mysteries have existed for so long. It takes a lot of hard work to get beneath the surface and figure out what's going on.

Josh Gates and Professor Pearce Paul Creasman with archaeologist Matthew Vincent dig in front of the Treasury in Petra. (Discovery)

It's so interesting that little is known about the Nabataeans. What are you most looking forward to when viewers find out who they were?

The Nabataeans are, so to speak, the unsung villains of this region. Everyone knows about the Romans, Greeks and Egyptians, but the Nabataeans controlled this vast trading empire several thousand years ago. They were truly the only people who could help connect some of the world's most important trade routes. Because they took center stage, they became incredibly powerful, but also sophisticated. What you see in Petra is a capital city carved out of solid rock.

All buildings have facades that were literally carved into the sandstone. So creating things like this requires a tremendous amount of technical and artistic skill. The Nabataeans borrow from all the cultures they come into contact with in everything they build. We see Greek and Roman influences in the way they build their temples and columns. In the middle of their city we see a Roman-style amphitheater. This was a highly developed culture and we know very little about it. They have largely disappeared into history.

The graves above you are empty, but if you go down you will find remains and 12 ancient skeletons. How surprised were you by these findings?

The discovery in this episode is beyond anything I ever expected. When you think about visiting a wonder of the world, you simply have no expectation that you can conduct such an excavation in such a significant place. Maybe you will find something so meaningful too. This is a huge discovery. Most of the graves in Petra were found empty. Petra was never really abandoned by the locals. Today the area around Petra is home to the Bedouins, but since it was never completely abandoned, many of these tombs were looted or cleared in ancient times. So when modern archaeologists discovered or rediscovered the site, or rather when the Western world discovered it, it was largely empty. A real mystery. One of the most mysterious things about Petra is the Treasury itself.

This is crazy when you think about it because it is one of the most famous buildings in the world. An image that we know from the Last Crusade and is one of the new seven wonders of the world. You can recognize it immediately, but archaeologists still don't know much about this building. They don't know when it was built, who built it other than some Nabataeans, or what it was used for. The name “Treasury” comes from the rumor that the great treasure was kept there, but of course there is no evidence of this.

Most people assumed it was a grave, even though no bodies were found inside. There are no inscriptions anywhere on the building that indicate what it was used for. Finding a tomb full of skeletons, which is so rare in Petra, is extremely important because the treasury was built on this tomb for a reason. This gives archaeologists a whole new list of clues to help them understand the above motivation for building the Treasury.

This is just your first adventure this season. What other journeys are you looking forward to taking audiences on?

It's a truly wild time of year and a true global adventure. We will travel to investigate, honest to God, pirate treasure off the coast of Cape Cod. Excavations with a team on one of the world's few authenticated pirate ships, owned by “Black Sam” Bellamy. We will examine the largely forgotten history and lost treasure of America's first train robbers, the Reno Gang. We will also travel overseas to examine the lost bones of Saint Nicholas. This is a great story that I'm looking forward to. This is the historical saint once associated with Santa Claus. In ancient times, its bones were actually stolen twice. There's this amazing case of what happened to the bones that became Santa Claus. It's a story that will take us from here to Turkey and Italy and even Illinois, where one of his bones may be located, which is a pretty remarkable thought.

What comforts from home do you always bring with you when you travel?

If I'm honest, my phone. We can no longer live without these devices. They are truly the only way to communicate. I keep my phone in my back pocket, which is very convenient for making calls and occasionally listening to music on long flights. I always try to keep a diary with me. I always tell people that if you write just a few words a day about your travels, it will be more meaningful to look back on than any photo you take. It's a fight. Ultimately, it's difficult to create a journal entry, but I've done it on most of my trips.

It's amazing that you've been doing this show for almost 10 years. How do you reflect on this milestone?

I think about this with great wonder and amazement because when we first started this show, one of the first questions we asked ourselves was whether there were so many mysteries in the world that we could actively pursue. It turns out it's a bottomless list. There is an incredible amount of work being done around the world to understand our shared human history. That's why I'm really proud of the show because it has allowed us to visit these explorers, scientists and archaeologists around the world who are doing sensational work.

I look back at some of the places we've been, from excavating tombs in Egypt to discovering a Mayan pyramid in the jungles of Guatemala. And I have to say, I'm looking forward to our season premiere. Going to Petra, one of the most famous places in the world, and being part of an incredible discovery is, in my opinion, one of our best moments in the series so far.

They did these live shows. I think it's the perfect time for the Halloween season, which is all about ghosts and monsters.

I've spent so much time abroad that I don't have much time to connect with people who support the show. A live talk is a great opportunity to connect with fans of the show, share some of these incredible stories from around the world, hear their questions and join in a conversation about discovery and the unknown. As Halloween approaches, everyone loves stories about the paranormal and ghosts. People are surprised that stories about ghosts and ghost hunting go back thousands of years. There are reports that the Roman letter writer Pliny the Younger wrote about a haunted house several thousand years ago. We have long been fascinated by the things that happen at night. I love coming together with fans and telling these stories and sharing this whole world of the unknown.

Expedition unknown Premiere, October 9, 9/8c, Discovery Channel