The idea behind this was to basically have a fanon version of the Sky Corridor from Frontier in the the New Monster Hunter Fanon Wiki. Just a bit altered and with a small plot twist added.
The Ancient Mines were discovered by some shepards as they where trying to bring their livestock from one valley over a mountain to an other valley behind it. One of the animals got lost in a crack and fell down. The shepards started looking for it and found weird structure walls as also wall paintings. After some more searching they found the lost animal and a gate. After the shepards crossed the valley they started telling the story about the cave and the weird structures.
The word spread and the Alliance quickly sent out some researchers to investigate about this new structure. Soon they returned wit good and bad news. The good news were that this structure was an almost endless mine going down deep into the earth. It was full will information from the Ancients and had lots of technology hidden inside it. The bad news were; it was full of monsters. Weird odd ones the have never seen so far. Some even resembled those they saw pictures from ancient scripts, books and wall paintings they found.
According to that the Alliance sent out some teams of hunters to go and find out what else is dwelling inside this Mine. But everytime they sent out hunters only a few came back. Due to this they locked and concealed the place as very dangerous. Only special hunters with allowance where to enter this place and also only under certain conditions. The Alliance named this structure "Ancient Mines" thinking it was a construct built by the ancients to gain minerals, ores and other riches from the earth. They speculated that one day monsters started to enter these mines and eat all the workers. The Alliance said that they could have imagined that the creatures back then started to nest inside these structures and make it a very special habitat. Once the humans where all gone nature began to create a very unique yet odd biological foodchain system, making it possible for monsters to survive there.
One day a very experienced hunter team out of 3 teams went deep down into the mines. Two teams of Hunters, one hunting party being melee weapons, while the other team was full of ranged weapon users. The third "hunting" Team were scientist and reasearchers. While the hunters dought the monsters, the reasearchers gathered as much info and data as possible.
Soon the Hunting party went deep down into the mine and noticed something, that this "mine" had a cylinder form. And that it had openings that could have been windows. That didn't make sense to the Scientists, so they started going deeper. With every layer they found new hints to this place that didn't add up. It seemd that the ancients didn't dig down, instead they build up. Into the Sky. But how was that possible it the Mine was inside a mountain?
Later the Alliance made a theory that the Tower was build first and due to weather, climate and also geological changes it became more and more a mountain, hence the confusion why people think it was a mine.
After the Exploration the hunting teams came back with only three loses. Two gunners being killed and one Scientist leaving himself behind in order to stay in the tower and continue to reasearch and also to help the others flee. It is still unknown if the left behind researcher is alive or dead. Though they found out that many ancient weapons and armors are hidden in this tower. But, there have been two kinds of armors. Only being very old and superior high andvanced packed with technology while the other series seemed less advanced but more "modern" even though still being old and advanced to todays standards. The further down they went the more dangerous the monsters became and the greater the infos where they have fought.
The Alliance have been also reported to find rooms full of bones, not from monsters but from humans. Meaning that this mine used to be really a living place for the ancients back then. Though it is still unclear what they did in that mine back then.
The Ancient Mines is a long and endless structure that has many rooms. Inside the Mine there are lots of traps, some working, some inactive, some deactivated, some jammed and also some that have been destroyed. While the hunter is able to descend down into the mine, he/she can explore and encounter monsters and gain rare materials and other treasure. In some cases the hunters are even able to find very rare armors and weapons, being held and protected by certain monsters.
There are two Series of weapons and armors: GX and NX. GX being the very old Series (Ones from the First Dragon War) and NX (being from the second Ancient Dragon War). GX and NX weaps have unique skill points in them. Meaning they can have not only slots but also skills implemnted into them. This could help getting rare and unique skills into a set.
After every hunt the player is able to collect data and post it on a scroll. During some hunts the scroll can be used to unlock certain rooms or activae tarps. Some rooms may have monsters hidden inside them or be empty, sometime players are able to recieve armors and weapons. The deeper the hunter goes the more scrolls he/she will need to activate things.
Traps can be used to break open rooms and make open a new path to discover or be used against monsters.