Without care for time, Rino explored the abandoned mines to his heart's content. It was not just a dwarven sleeping quarter or a fortress. The dwarves took the time to make it their home before it was abandoned.

Rino found out what those small tunnels with wire meshes were. They were so deep into the heart of the mountain that there wasn't any fresh air. Without a constant air supply, the dwarves would have suffocated a long time ago. Rino failed to consider that because he was an undead and forgot all about breathing.

The small tunnels in the floors were slightly different, and they worked as drainage. Rino created a small clone that found out where all the sewage went. He wasn't sure if he should support the idea of dumping waste into the sea, but that shouldn't make too much of a difference now because nobody was living here. He only hoped that the dwarves did not dump the more toxic materials into the sea they used in smithing.

Over the next three days, Rino mapped out most of the mine. There were only a few routes left unexplored because the ceiling had caved in or it was left unfinished. Yet, the lich could not help but feel like some things are missing.

Sure, he saw their sleeping quarters, storage room, mines and even their grand furnace room. However, the earth gnomes told him that the dwarves left behind great secrets in this abandoned facility. Everything that he saw in the last few days was too ordinary to be considered a great secret. Something was missing.

Suppose there was something that the dwarves did differently from the monsters and other species that Rino encountered in his short time after arriving in this world that impressed him. In that case, it must be the unified written language and development of mathematics.

As Rino paced around in the smithing workshop, he took a look at the rusted and broken tools. Many functional casts and moulds were lying around that would be handy for future uses. He had a feeling that the gods would eventually ask him to venture into metalwork after he finished the pottery and masonry phase.

Secret entrances looked like the main theme for this fortress. It was understandable why the dwarves would hide so much of their research and important things. If their enemies were as powerful as everyone claimed, it was only right that the dwarves took extra measures against them.

Rino only found the smithing room and grand furnace after tracing his steps back. He almost missed the signs of a secret entrance when he was busy mapping new storage rooms. However, after a while, the lich started to understand the signs he was looking out for.

Mutt's nose was convenient and could often smell when there was an active air flow in a room that did not come from the vents. Rino would use that knowledge to search for hidden levers, switches or doors. The dwarves loved hiding it behind iconic things that often were missed by others.

Rino found the lever to the grand furnace room behind a rusted chainmail armour display. He found the switch to the smithing room inside what appeared to be a golden vase. The golden vase was affixed into the cave's stone wall that acted as a display shelf. Initially, Rino did not think much about their interior decorating tastes, but after a while, he realised that the dwarven hospitality differed from those of pompous nobles.

These stocky engineers did not believe in displaying useless items around. Symbolic items that boasted of history were always a dead giveaway about more secrets to discover. Rino enjoyed the rich culture, history and heritage that scattered all around this labyrinth of a mine. The dwarves proved to be the most intelligent species so far, apart from Kragami. While they did not know magic or prove to have any capacity for it, they were on par with Rino when it came to curiosity.

It was such a shame that Rino could not meet them while they were here. He imagined that they would enjoy each other's company quite a bit. With Rino's knowledge about alchemy and their advanced engineering discovery, the kind of things he could introduce to this insipid world was endless.

The layout of this mine was rather simple, but Rino decided that it was overly simple. He missed out on several spots, and based on his guesses, they were either undiscovered locations that he had yet to find entrances to or dull duds that the dwarves did not hollow out because of some mishap.

He took the time to investigate some of the collapsed entrances and unfinished building projects. The dwarves did not fix them or left it that way deliberately, even while they lived here. Rino concluded that the mines were designed to be sturdy for at least a few centuries before decay set in for the beams to collapse into the mines.

Probing a little further using the power of shadows and clones, Rino learned the reasons for the unfinished projects. Some roads were deliberately sealed off because of dangerous gas and poison. The area was blocked to the best of their abilities, while others were abandoned because of hard rock that broke their tools.

To Rino, those rocks were easily broken using magic. However, the dwarves found it impossible to mine through those areas. The paths they constructed would either bend around the hardened areas if they did not cross into other sections of their caves, and if it did, the entire project was called off, and the dwarves would look for a new spot to start digging.

The black rock that the dwarves abandoned was actually a mana absorbing crystal that was often used to shackle dark magicians in his previous world. The stone would absorb an insane amount of mana from the magician constantly and disperse it safely into the air over time, causing the magician to be unable to cast any spells. Naturally, Rino was probably the only magician who remained unaffected by those shackles. His natural mana reserve was big enough to single-handedly take down dragons. Such crystals meant nothing in front of raw power.

The pickaxes that the dwarves used were usually fashioned out of a metal alloy that Rino knew back then as steel. Steel was an important discovery back in his world that made the dwarves a race not to be underestimated. The humans often used iron or stone pickaxes that were easily dulled or shattered. The steel forged by dwarves lasted almost ten times longer than the regular pickaxes. In addition, they were the only pickaxes without enchantments that could mine the mithril that the king wanted.

Figuring that staying here wouldn't help him, Rino went back to the room that spoke volumes about the dwarven history. Instead of using paper, the dwarves opted for finely sanded stone plates to record their history. They carved their story into these thin stone plates and arranged them in a huge room full of mined out shelving, creating what Rino knew as the very first library in this world he chanced upon.

Unable to read dwarven tongue, Rino could only make guesses from the illustration. The good thing about the dwarves was their ability to draw accurate diagrams and illustrations for their blueprints and schemas. Most of the archived stone plates were research journals and sometimes dairies. Rino wondered if anyone would be kind of enough to draw a map somewhere.

He saw the sketches for flying machines with indications of the actual sizes. Rino figured out how the dwarves wrote their numbers after a while, but understanding letters and the language was harder. Mathematics was somewhat universal, after all.

After what appeared to be an eternity of dusting stone plates, Rino found something that contained more information about the weapons the dwarves were trying to create. At the same time, he saw a very detailed illustration of those jellyfish monsters he saw when he was in the jungle.

The swords that were effective against the jellyfish monsters were mentioned in that stone plate with some very specific temperature indications and a furnace illustration. Rino decided to store this plate in his inventory to decode leisurely when he returned to his study.

In the meantime, the lich went around to look at every stone plate in the library. Snippets of history were also recorded on these stone plates. Rino guessed that these stone plates in the section he was in recorded the war against the Harvesters. The numbers at the top of the stone plate could represent the date, and in it, Rino saw some other numbers that increased with time. If there was a single vocabulary he might have figured out in dwarven tongue after looking at so many records. The word had to be "Harvester".

By the end of his library raiding session, Rino learned a few things. Those jellyfish monsters were indeed "Harvesters" who ate the living and turned them into a vegetative state that he witnessed in Zerg's village before he razed it.

The dwarven tale gave him a better overview of what happened to this world. The illustration of winged beings that Rino assumed were gods sent these harvesters to collect something from all species. Humans and more intelligent life forms were often attacked, and the dwarves fought back by building this fortress.

The harvesters were very powerful, and like ghosts, they had no weakness. Souls were reaped, and they cannot be harmed or outrun when they arrived. However, the dwarves discovered that weapons forged from the fire could hurt them, and while the weapons forged by fire did corrode after time, a harvester could be killed. The number of times a regular weapon could be used was five times before it disintegrated. However, according to the weapon designs, the dwarves might have found a way to create weapons that lasted a little longer and dealt a lot more damage, although Rino had no idea where they were hidden.

Last but not least, he confirmed the reason why the dwarves left the mines. The harvesters broke in from the small tunnels that brought in the fresh air and tossed sewage out. That was before they added wire meshes. It attacked a good number of dwarves before the dwarves finally killed them all. With an all-time high casualty rate, the dwarves found themselves unable to sustain themselves.

Illness, starvation, suffocation, and all sorts of problems started when the dwarves lacked the manpower to maintain this fragile underground ecosystem. Eventually, they were forced to abandon the mine and find a friendlier environment to migrate to. Nobody knew where they went, but Rino read in their library that they chose to go in different directions in various groups to increase survival chances.

Now that Rino knew there was a powerful weapon somewhere in this mine capable of bringing down Harvesters, he made this his mission to find it. All he had to do was look for the correct signs.

This shouldn't be too difficult, right?