This Thief fan mission has you play a blind character trying to steal back their sight, and honestly that's probably the least weird thing about it

I think I just ate a compass. By that I mean a magnetic one, not a pointy one used to draw circles. I'm not stupid. I just can't see, you see, and when you can't see it's a lot harder to tell whether an object you just picked up might be edible.

Hence, when I plucked a star-shaped object off a door and my inventory labelled it as "food?" as it does with everything, down it went, costing me two points of health and any chance of knowing where north is. Not that a compass would have been much use to me anyway, given the whole lack of vision thing.

This would probably be the weirdest thing to happen in most games. But in Selection Day, it doesn't rank within the top ten.

I first heard about Selection Day via Romain Barrilliot, the Arkane Studios level designer and mastermind behind Thief Gold's excellent fanmade campaign The Black Parade—who recently helped me figure out how tall Thief's protagonist Garrett is. Selection Day is a newly released fan mission (or FM) for Thief 2, which Thief's relatively small community has produced thousands of since the first game launched. So when Barrilliot described it as "one of the most unique I've ever played", I knew that I had to try it.

Selection Day takes place in the far-flung, post-Metal Age future of Thief where the City is plagued by two possibly-linked epidemics—sinkholes and blindness. As the sinkholes transform the city into a jumbled, semi-ruined labyrinth, the blind are guided through the maze by an elaborate braille system. This involves traditional signs with patterns of raised bumps, supplemented by strange eyestalks through which the City's unseen masters (known as Ocular Superiors) communicate. There are also machines that project braille into the air to lend primordial vision to those within proximity—one of my favourite nuggets of Selection Day's tremendously involved worldbuilding.

You play as a court judge on their way to preside over an important ruling, when an Ocular Superior unexpectedly leads you to crash through the window of a mysterious building. Here, you are given a simple objective "Seek Remedy for Your Blindness".

Naturally, playing as a blind character has major implications for how you experience a Thief mission (as it would for most games, given how visually led the medium is). But it's important to point out that your blindness in Selection Day is not total. Since the building you're exploring has one of those atmospheric braille machines, you can see the outlines of rooms and objects at short distances. However, everything is rendered in texture-less black and white, so identifying objects often means moving close to them to "feel" out their shape.

You also can't judge the difference between light and shadow, which is kind of important in vanilla Thief. As it happens, Selection Day is more of a puzzle-box than a traditional stealth mission, to the point where you start without Thief's weapons or equipment, and most don't feature in the mission at all. But there are still a few guards milling about that you need to avoid.

As such, sound plays an even bigger role than it does in a typical Thief mission. Not only is listening to floor noises and guard cues vital to avoiding detection, but ambient noises can also help you identify where exactly you are in the building. And Selection Day's use of Thief's sound propagation system is exceptional, even folding it into several puzzles in ingenious ways.

Considered alone, these dramatic changes would make Selection Day stand out. But Selection Day deploys its blindness concept to superb effect. As you creep furtively between rooms, your mind begins to fill-in the outlines that surround you. Yet rather than elucidating your situation, it only leads to further mysteries.

Why is this room filled almost entirely with drawers? What's with all these pipes and lenses? Why does music start playing when I push this button? Why can I hear monkeys?

Sometimes, the answer to such questions is a punchline. For example, in the centre of the map is a hall lined with paintings. But whoever wrote the plaques for the paintings must have been blind like you, as they are speculative rather than descriptive, with lines such as "Probably a landscape" and "We prepare ourselves for a masterpiece".

In another instance, I discovered a secret door in a room lined by oblong shapes, which led to a strange pool buzzing with flies. As I waded about searching for clues, I realised that the oblong shapes I'd passed were almost certainly toilets, and I was in all likelihood splashing around in a septic tank.

Other times, solving one of Selection Day's puzzles will lead you to wild new spaces. It's hard to explain how Selection Day unfolds without spoiling it. But safe to say, the map becomes way more surreal than what I've described so far, playing with your limited sight in ingenious, often devious ways.

What's most impressive, though, is that by the time you encounter these deeply bizarre spaces, you've probably fully bought into what Selection Day is selling. Selection Day's map is by no means the biggest FM around, but its fiction bleeds deep into the earth. Even when it defies explanation, it feels like understanding is only just out of reach.

It's a striking work of imagination, though I will say Selection Day doesn't always make itself easy to appreciate. Some of its puzzles are obscure to say the least, while certain navigation challenges later in the mission will see you die a lot in order to progress. Strong saving discipline will help alleviate the worst of the pain. But you should still set aside a couple of hours to pick your way through its conundrums.

If you want to try Selection Day yourself, you'll need a copy of Thief 2 patched up with T2fix, and an FM launcher like Angelloader. Note that Selection Day's designer, Hanover Aldercash, recommends the FM be played in 1080p, as higher resolutions will increase the view distance and diminish its vision-based puzzling.