Fionn gazed out the transport’s window at the landscape of the moon before him. Empty and lifeless. Unfalteringly strange. Four months into his time here and somehow it was yet to become familiar in the way that anywhere on Earth can be. He wondered why that was. He figured the knowledge that being out there meant immediate death must trigger some kind of repulsive reaction. He didn’t know if that was a universal truth, but he felt it might be true for him.

He had felt like an imposter the whole time he was here. A base filled with scientists, and he was the handyman. His title was grander than that, but that was all he really did, it seemed. Fix lighting, change filters, ensure everything is oiled. It paid well: he liked the work fine. He still felt like he was a fraud being on the moon, that surely someone with a greater destiny should be here.

But today was different. Today was the first time he had cause to leave the base. A surveyor searching for water had got stuck somewhere. It seemed to have found evidence of water density, then stopped signaling. The popular hypothesis was it was trapped in a cave – apparently it had happened before he arrived. He was sent to go find it and reset it. No great deal, but it was a trip out of the station.

The transport took its time, so he watched the moon go by. Seven hours to the surveyor, probably five minutes to correct the problem, then seven hours back. He looked at the landscape, read, even slept for some. He needed to be rested and prepared for unforeseeable difficulties in trying to rescue the surveyor from the cave, or whatever fate had befallen it.

Eventually, at the far end of a great flat dusty plain they crossed, the transport started to slow down and descended a slope. Fionn was surprised, as he had presumed that it would be too steep, but the descent seemed almost perfectly measured. Eventually it arrived at the opening for the cave. He suited up and exited the airlock, and found himself staring at the cave’s entrance.

It was round. Almost perfectly round. He had seen nothing like that on the moon before. He had expected some kind of billions of years old half collapsed hollow created by lava, but this was too perfect. Had he not known better he could have described it as man-made.

He walked inside the cavern and looked around. Aside from debris here and there, he probably could have taken the transport in. He scanned for metals and the device went off the charts, so he switched it back off. Must be because of some kind of ancient meteorite strike nearby. Strange that the tunnel was still intact though.

Eventually, he came across the surveyor. It had powered down, having crossed a small pile of rubble it couldn’t get back over. He tenderly lifted it back over the debris and reset it. It power cycled and was active again in under a minute. And then - the strangest thing - it returned over the rubble and carried on down the tunnel. Fionn clambered back over the rocks again and followed it.

The surveyor moved at a speed he did not expect. It had clearly been this way before and scooted around the random detritus on the floor. He had to walk pretty briskly to keep up – difficult when wearing an Environmental suit. His beam of his flashlight seemed to disappear into further abyss.

The surveyor stopped abruptly, and its lights flashed – it had come to the end of the cavern. But Fionn did not see it stop and almost fell over it. For the previous twenty or so paces, he had stopped looking at the little surveyor. Instead, he looked at the reflective dome above him.

It made little sense that anything this smooth looking should exist on the moon, much less beneath it. And in places, he could see that his light travelled beyond it - was it transparent? Covered in millions of years of dust perhaps? As the idea that it could have been a structure built by sentient beings crossed his mind, it was clear that it was a tunnel, not a cave.

He was further stunned when he saw that the little surveyor had stopped at what looked like a giant airlock and was looking at a button with a faint light signal beside it. He instinctively touched it and two giant doors opened. The surveyor waited for his reaction.

Fionn tried his radio, but there was no reception. Dismissing the alarms in his head, he stepped through it and shone his light further. He looked around and saw it was a more confined space. Opposite the door he entered was a match to the first button. He felt like he had no choice but to keep going now. He pushed the button and felt a gush of gas around him before the next door opened.

He stepped through it into a vast dark world. Nearby, he saw what looked like crumbling buildings, and some form of transport network. Distantly, could discern what must have once been a great city, surrounding a lake that was still mostly liquid. Life thrived here once, before dying several million years ago.

It occurred to him that this was probably now a mausoleum, a testament to a great civilization long lost, a tomb to a people who had one time lived and one day died. He was awed by being the first human to visit this great chamber. It was only after years of research and study was concluded, that anyone realized that he was not the first born of Earth to see the city, just the first since the start of the Cryogenian Ice Age.