Space Artifact - Halls of Doors

Dreamed I was on some sort of station in orbit around the Moon. An asteroid had been found with some sort of ancient construction in it. The asteroid had been hollowed out and living quarters and labs had been fitted throughout the long tube that had been carved through the center of the rocky body. What was odd about the thing is that it had a gravitational field on each of the four "walls" of the tunnel. Each wall had cubical farms in the center, and along the outer edge of each was a section of doors, or portals.
The doors, about 8 feet wide and slightly less tall were in a raised square cross section that ran the length of the tunnel. There was a door about every ten feet, so there was less than a foot between them. Each of the doors had many indicator lights and screens of data, most were inactive. All four sides of the tunnel acted as a floor, and each of the four tunnels had doors on each side.
There were rails that you could climb that would take you over the square cross section holding the doors, and would allow you to shift to the new direction of the gravity. You could look up and see people walking through the halls 80 feet or so above you. Some of us had rigged ropes up through the center of the habitat areas, just to have the experience of climbing up and through the zero G point in the center of the tunnel. We also ran a steel cable through the center so you could move from one end of the artifact to the other. (The tunnel was just over two miles long.) One of my many jobs was to fly the "Crane" an aerodynamic space hybrid that was capable of hovering like a helicopter or space ship. It was tethered to the central cable most of the time. I had helped build the vehicle and had come up with the telescoping counterweights that allowed us to hover over any part of the station.
When we'd found the place, it had been vented to space, explosively, from the inside. We'd managed to retrofit some airlocks on either end and fill it with atmosphere. (Ours was different than the remains of atmosphere we detected in sealed rooms.)
The section with the doors had an edge on each of the four with bright light that kept the entire place in near daylight. The color of the light was slightly greenish, the plants seemed to like it a great deal. We'd been in the place for over a year, and had never been able to open one of the doors yet. We'd managed to get readings of activity on a couple of dozen, though.
One of the doors opened on its own, and beings from another world exchanged radio data with us, and we soon had a mathematical understanding, a time and place understanding, but not much else. We were not making much headway until we finally deciphered a warning. (We thought it was a warning, it used the number 81 and connected it to the symbol we interpreted as their people, then the number in the next few transmissions diminished rapidly down to 9. The sequence repeated three times, and then the information with the door and date, which was counting down, then the warning frame again.)
"UNTRANSLATABLE is returning," with a door number and a date in the not too distant future. As you can imagine, this caused a great deal of panic, even in a group of folks partially chosen for their level headedness. The door slid closed with little warning and no way of stopping it. The materials the door was made of only slowed little at the steel wedge we'd inserted. (It housed our probe circuitry.) It did hold the door long enough to witness the portal disconnect; leaving the station it had connected to and drifting into interstellar space at an impossible rate.
It took us a while to figure out their door numbering system, and once we did we cleared the station for 100 feet in every direction from that door. Heavy weapons were brought in and assembled on the floor across from it. Marines were trained and brought up from Earth. On the date of the door opening the artifact was abandoned except for Marines and a few volunteer scientists, as well as a few of us technicians. All of us were armed. As the evacuation occurred several of the more panicky types continued to argue that we should blow the airlocks as a precaution. That had been considered, but the feeling was that Space Suits were too difficult to allow for effective operation of the soldier's equipment. I was in the small craft that we used to move equipment through the center of the artifact's zero G area. I had a Marine in the jump seat with a pulse laser drill. We swooped slowly through the tunnel, turning and looping back from a couple of hundred feet on each side.
I was checking on the status of the emergency evacuation tubes we'd installed Each one would take one or two people and seal them and launch them towards the airlocks on either side of the door. For speed's sake we already had the inner freight airlock doors open on each side of the artifact. We could be removing about a dozen at a time; shuttles were on the other side of the locks. Or, depending on how bad things got, we would blow the locks outer doors and shuttles would recover the life pods as they could. We'd calculated that most would go into a high looping orbit around the moon and be relatively easy to recover.
Below us the door indicated a positive pressure difference, we'd figured out how to read some of the indicators. The door slid open. Heat began to pour in through the opening, the temperature was about 180 degrees on the other side. A marine commented that they were looking into the mouth of Hell. "Something is coming!" another one warned. We were not in a position to see through the door, and the monitor though about 17 inches, didn't give much detail through the swirl of heat. It did look like a long tunnel much like this one only with this door in the end of the tunnel rather than along the length. Several of their doors were open. The floors of their tunnel were pockmarked and melted, something we hadn't been able to accomplish. There were shapes moving in the doorways. Unlike our tunnel, nothing indicated, to my eyes, that the floors were inhabited at all. Marines started praying, the first alien object pulled itself through the doorway and I could see the air behind it sparkling with a laser beam back into their tunnel.
"They're using lasers instead of radio," I commented to no one in particular. I tried to get a data read from the flashing light, but my systems were not sensitive enough to make out any data.
"Incoming!" came the shout from the floor across from the door. I switched the camera view to their position, a door shaped object with an accordian front was accelerating towards the door at an angle that would land it on the tunnel floor opposite the door, roughly in the center. Science operatives on that floor pulled back behind bunkers. Just in time. The object burst through the door, lasers pulsing in every direction. I shot past us, missing us, but melting holes in our counterweight system. I was able to maintain control.
The invader slammed into the wall/floor on the right and the front end collapsed. As it did so it blew small pods out in every direction. Bunkers vanished where the pods landed.
Missles streaked from a few survivors racing through the doorway, knocking the next intruder aside enough to cause it to collide with the doorframe on their side of the door. Several missile impacted on it and knocked it aside (too bad I thought.) My gunner was drilling the intruder below us for all he was worth. Hot orange gouts of molten something spurted from the alien device where our pulse laser struck it. I gave him the ten minute powerdown warning and took evasive action as it swiveled around to fire lasers at us.
I pushed the throttle and hooked us into the center cable just as our thrusters were holed completely. The pulse laser batteries took a direct hit, even through the plating. I ejected, the Marine and I turning the silvered underside to our attacker. I hoped it would be enough. We must have drifted outside the devices firing angle, as it continued to pour fire into the body of our craft until it disintegrated, parts of it falling in all four directions.
I realized the young marine had been shouting at me, wanting to keep firing with his sidearm, until he saw the craft explode like fireworks, then he got very quite and just said, "Good call, sir."
I wasn't too sure how good the call was. We were headed for the central airlock on the far side of the artifact, but not fast enough to get there if more broke through, too fast to stop for a regular airlock cycle. I was trying to work out the timing on getting us out, but could see that wasn't going to work, I could hear air movement, our pod had take damage after all. While I had an airtight suit, the Marine didn't (His armor did have a sealable hood with a viewplate in it that would allow him about 3 minutes to get to auxiliary air or a life pod.)
I Started clamping the brakes on the cable and started lowering us into the gravitational field.
I noticed that there were other doors lighting up. As we came down in the hallway of the wall opposite our invader, I checked the door status, looping through the survey cameras, most of them had vacuum on the other side. I hoped our side of the door wouldn't open. I heard explosions and more missiles firing from behind us, but couldn't turn around far enough to see what was happening. The marine told me they'd stopped another one in the doorway. We broke and ran back towards the action, because that's where the escape pods were located (my reason) and that's where the action was (the Marine's reason.)
As the dream faded I heard someone shouting "they're back!" and on my channels scientists saying they've begin to decode the door control signals the invaders were using to activate our other doors. "Great," I thought, "If we survive we might have some idea of what to do next time."