I played the 21 worst Thief missions in existence and had a far better time than I expected

Quamtotius Purgamentum begins in the time-honoured tradition of all Thief missions, with protagonist Garrett screaming loudly as he falls through an enormous hole. Landing inside a giant blue cube, he is immediately accosted by a half a dozen guards, some of whom spin violently in the air like a helicopter's rotors.

Garrett's only chance of survival is to crawl through one of four square holes in the cube, leading to various rooms connected by twisting corridors, illuminated in Thief's hallmark magenta. One room is a zombie-slaying arena set up by Garrett's evil twin brother, Barratt. Another contains five bottles floating in the air, and a text decal on the wall that simply reads "art".

Without a shadow of a doubt, Quamtotius Purgamentum is one of the worst Thief missions I've ever played. And that's the entire point. The mission was submitted to the Thief mapping community's Total Crap competition, which ran in late 2006 with the aim of creating the most heinous Thief map possible.

Over the course of several weeks, the community committed 21 crimes against level design, and over the course of last weekend, I decided to judge them all.

Why did I do this? Well, if I felt like justifying it, I'd write something like "The Thief series is synonymous with excellent level design, so deliberately trying to make a bad Thief map is an interesting experiment, one that may yield fascinating insights into what precisely makes Thief levels great." Yes, that sounds convincing.

Mainly though, I thought it would be funny. And it was funny, but not quite for the reasons I expected. It turns out the Thief mapping community would be better off ditching the blackjacks and taking up new careers as alchemists, as it's surprisingly adept at turning shit into gold.

What initially surprised me about the competition maps was the diversity of crap on show. In my head, bad Thief maps would run along similar lines. They'd be very square, overly linear, lack sufficient places to hide and so forth. Yet out of the 21 maps created for the competition, only one sort of takes that route.

Simply called 'bad man', this map puts Garrett in a brutal survival gauntlet he's entirely unfit to face, pitting him against crowds of combat bots, tree beasts, and haunts that move at ridiculous speeds. It is virtually unplayable, but this in itself makes it amusing. Moreover, the part of my brain perpetually cursed by Dark Souls enjoys the preposterous challenge.

Outside of this, the most straightforwardly bad maps upend Thief's core mechanics, such as The Scary Castle. This basically transforms Thief into a standard FPS, with Garrett ascending a tower filled with haunts, blasting them with fire arrows as he goes. Similarly, Chuffy Train assembles an impressively unsightly locomotive out of Thief's blocky Dark Engine, and fills it with civilians that Garrett must brutally slaughter to complete.

Alongside these are missions that play on amateurish 'My first level' designs. Quamtotius Purgamentum is one of these, but others include t0t 1: The Escape, a deliberately half-finished affair with sparse environments and rows of T-posed zombies.

Then there's Walkin Da Moon, wherein Garrett travels to the lunar satellite of whatever planet Thief is set on to steal 10,000 gold from a race of moon spiders and assassinate their king (what a premise). Overall, this map does a great job of being terrible, if that makes sense, but it undermines its own lack of quality by including an impressively sculpted steampunk lunar lander.

In this manner, quite a few maps inadvertently snatch defeat from the jaws of victory. A Long Way Down transforms Thief into a vertical platformer, with you descending from a lofty rooftop down to street level. While technically a bad Thief map because it doesn't engage with most of Thief's core systems, as a ten-minute diversion, it's surprisingly fun.

Others fall at the first hurdle. Having Regrets flips the whole premise of Thief on its head, requiring you to return the items you've stolen to their rightful owners, before heading home in shame to "think hard about your actions". This is a brilliant idea for a Thief FM, and as such immediately rules itself out.

There are also a couple of missions that are just too, well, good.

The Kill Factory places Garrett onto a Looney Tunes-style conveyor belt riddled with crushing traps, complete with a reworked cartoon art style. It has about as much in common with Thief as Pokémon does, but it's also way too accomplished to be bad.

Likewise, The Cube traps Garrett inside a maze of deadly traps inspired by the film of the same name. It's by no means a pleasant map, but its deathtraps are all imaginative and cleverly put together, clearly designed by someone who knows what they're doing.

But even the maps that are shoddy and slapdash are often so in a way that's entertaining. This is partly because the designers are playing the competition for laughs. Irony, in-jokes, and internet humour abound and are frequently deployed to great effect.

One mission, called Shadows of Darkness, shoves 1,000 flares into Garrett's inventory on the mission preparation screen, which made me hoot with laughter.

My favourite entry of all, simply titled Tcrap, places Garrett in a pitch-black environment with perilously slender platforms, with the simple objective "grab a coin". If you succeed in spotting the coin, moving to it without plummeting to your death, and retrieving it, you're rewarded with a new objective: "grab another one". Despicable, I love it.

Despite the tongue-in-cheek nature of many of the maps, the competition nonetheless demonstrates that it's surprisingly hard to make something bad on purpose.

Most of the levels attempt to undermine Thief by pulling it out of context, but the intent behind this choice means the mappers end up making something interesting instead. Unpolished and wonky, perhaps, but conceptually intriguing. The supreme irony of putting a line of cups in the air and labelling it "art" is that, yeah, you kinda did just make some art. Truly terrible art requires the creator to be wholly earnest in their intent, yet oblivious to their lack of talent.

With that in mind, which of these maps is truly the worst?

At the time, the Total Crap competition awarded its dubious first prize to a map called Incubus. But I disagree with this decision. Incubus is a multi-level surrealist masterpiece that includes giant guards and a medieval disco.

A more obvious candidate would be Hammerite Hideout, which is genuinely the creator's first FM, cleverly using the competition as cover for any genuine lack of quality. However, it's too self-aware and carefully constructed to be in the running for the worst.

In the end, my pick for the worst of the bunch would be OMG Get You're Blackjack Back! LOL. It's the map that most closely resembles a normal Thief mission, taking place in a small cluster of streets with multiple buildings to explore, but all designed in a wilfully shoddy way.

It's very much done deliberately, with a lot of zany elements like doors swinging open vertically and inappropriately applied wall textures. But it also features fistfuls of mid-noughties internet humour which have dated poorly, and this lends its crap-ness an authenticity that the other maps lack.

Did I learn anything from this diversion? No. But I had a great time. And I'd say these maps are worth playing just to see the many ways a talented community can spin the concept of a terrible level (even if their purported naff-ness is sometimes debatable).

If you fancy excavating this peculiar mapping septic tank, all the maps are still available to download. The maps are all designed for Thief 2, so you'll need a copy of that to play them, patched using T2Fix. Finally, you'll need a Thief fan mission launcher. I use AngelLoader, which is easy to set up.

There are, of course, far superior Thief fan maps you could spend your time playing, like the astonishing unofficial Thief 1 campaign The Black Parade. But if you're thoroughly taffer-brained and fancy some more light-hearted larceny, the Total Crap competition will provide a chucklesome afternoon.