Let's do another "classic," another nice big one and another of my old favorites! SCP-1555 is a mysterious, subterranean and fully automated factory of unknown origins and purpose, which periodically launches projectiles from above-ground cannons. This sounds fairly menacing until we're told that these projectiles are almost always aimed at empty fields and almost always contain nothing but mice. Ordinary, non-anomalous, live field mice. The collapsible log of observations shows how the facility seems to "experiment" with different techniques but rarely deviates from delivering mice, whether thousands and thousands of them pouring from a canister for hours straight or a handful of tiny single-rodent cartridges.

The maddening strangeness of this is pretty fun, and it almost doesn't need its exploration log to be mesmerizing...but that exploration log is one of the most interesting and even among the most frightening reads in the foundation.

On the outside, it's only a factory that shoots mice out of cannons. On the inside, it's pipes. Lots and lots and lots and lots of pipes, tangles and tangles of them, and channeling a seemingly meaningless variety of liquids and gases. One pipe labeled "make-up gas" is filled with vaporized lead, while a pipe labeled simply "emulsion" turns out to be filled with yellow, latex paint. Naturally, at least one pipe later turns out to be filled with mice, though another turns out to be filled with only mouse hair. Is this place MAKING the mice before launching them?

Soon, the team comes upon the first of many nuclear reactors, the kind more typically found in a military submarine, and many other, increasingly hazardous oddities. A staircase with uninsulated electrical wire for a guard rail, a hallway that slices matter into tiny particles, areas where the atmosphere impossible changes without any physical barrier and even a wall completely covered in open, functioning gun barrels. It's not just that the facility shows no sign of human activity, but that it's actively designed for nothing human to function within it for long...and its layout can even change when nobody's watching.

The facility eventually begins to feel more like an entity than only a setting; an ambiguously conscious and malevolent antagonist toying with intruders, and the final reveal, what awaits the last survivor when they return to what should be the exit, is just too good to spoil in a review some of you are going to read first. I'm onto you!

The great thing about 1555 is that we know what it does. We know that all this machinery supports a system that distributes field mice and that the different substances piped through it are probably used in the varying designs of field mouse distribution canisters, but we don't know why a facility would exist to do such a senseless thing, and probing deeper into it only makes it more confusing. The sheer excess of its scale, its power supplies and its defense mechanisms, all for that single ridiculous purpose, remains one of the most intriguing ideas in the SCP archive even years later...though I have to give it a four out of five this time, because as much as I love this kind of unexplained weirdness, a part of me does wish there were one more hint to latch onto.