Doom modder Ben Mansell made a level for Doom 2 that is so big that it takes upwards of an hour to complete. Probably a few hours for most on a first run.

Dubbed Foursite 4-in-1, this colossal stage is practically a campaign in its own right as it links four already giant levels together to one central hub.

Each of the four stages-within-a-stage culminate in a "boss room" with especially hazardous obstacles. Each of the four quadrants has a different visual style and enemy types. Once a key is acquired from each of the four quadrants, the door to the final boss can be unlocked.

Mansell noted on Reddit that it took his friend three hours to complete Foursite on their first run. Based on Mansell's 66-minute playthrough below, I can believe it. (Bear in mind that this is the designer running through it, so he knows exactly where he's going and what to do.)

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It sounds basic, but there's a lot of complex level design in this colossal labyrinth, with various killing floors consisting of moving platforms and shifting gears.

"A recent trend in Doom mapping, as computers get ever more powerful, is to create so-called 'Slaughtermaps', where it's the player and a thousand enemies in a single room. It's a perfectly legitimate style of play, but I always enjoyed the more environmental elements of the original games: the complex levels, the non-linear progress, the environmental storytelling," Mansell told me over Skype. "So I tried to build a map that didn't just rely on shooting enemies for the enjoyment.

"I think the ideas I'm most proud of are the environmental ones: for example at the end of the first quarter there's a room where you have to run across platforms while Mancubi shoot at you. That's the kind of environmental puzzle you don't get in that many modern Doom maps. The very last room too (forgive the spoiler!) has you dodging between moving platforms trying to keep out of sight of a final boss that never stops shooting you. It's entirely a timing based puzzle, and feels quite different to a lot of what else is out there."

Intriguingly, this Mansell's first Doom map and one of his only experiments in game design. He's not a developer, but rather just a huge Doom fan looking to make his mark in the world.

"It was very much a hobby for me, a few hours a week over the last year or so," he said, noting that the full level took around 300 hours to build. "I've always wanted to do something creative, to make something other people can enjoy, and I guess it seemed like a Doom map was my best shot at making something decent!"

Mansell noted that his only background in level design was "dabbling" in Quake 3 and Doom 3 back in the day, which is when he brainstormed the core concept behind Foursite.

"I originally doodled the design for the map (four wedge shaped quadrants around a central corridor) during an accounting lecture at university in about 2003, back when Doom 3 was new and it came with a map editor," Mansell said. "I never did make the map (I was never good enough or had the time), but the general idea hung around at the back of my brain. When I decided to make a Doom map, it seemed like the only option of what to make. It ended up being so big because it just felt like it had to to live up to the idea I'd been carrying around for so many years."

When asked if Foursite was made in hopes of attaining a career in game development, Mansell said it was mostly for fun. "I've found it a very enjoyable process, and was really amazed by just how active the Doom community still is," he said. "For example the level editor I used, called GZDoom Builder, is still being actively improved by its developer. New source-ports and features appear pretty much constantly, so it still feels like a very fast moving community to be part of, even for a game that's so old.

"I think Doom still has a bigger modding and mapping community than even something like Quake. Partly because it's a simpler game, so is easier to play around with, but also I think the core gameplay has that kind of arcade simplicity that doesn't really get old."

You can download Foursite 4-in-1 from ModdDB. Note that it requires Doom 2.