The basement is a primary setting of Letterkenny, the base of operations and primary meeting place of the Skids, their other base being the dollar store parking lot. The official name of the gym is coincidentally "The Basement," but it is never referred to as such.
The basement is where the Skids manufacture, store, and consume a variety of drugs, and sometimes deal drugs from there as well ("Letterkenny Spelling Bee"). It is also their refuge, however—the Skids are looked down upon by the Hicks, the hockey players, and Tanis and the Natives, leaving them few places to go in town without fear of harassment. When Katy accompanies Stewart there on a visit, the others are resentful, and the interloping of Gae and later Tanis are alarming. When Devon disappears, Stewart is bewildered as to why.
He had everything here. Hours upon hours of ultra-competitive gaming laced with hip-hop karaoke. Add a dash of late-night loitering and a splash of petty vandalism. And what have you got? Utopia. Arcadia. Kingdom come! — Stewart
Besides drug-related activities, the Skids spend countless hours in the basement playing video games, notably classics of older systems including the original NES to the original PlayStation.
The basement is cluttered with furniture which mostly appears to be castoffs, although Stewart prides himself on having an adjustable standing desk ("The Ol' College Try"). The room is cluttered with drug paraphernalia, video game consoles and accessories, and audio equipment, and its walls are covered in cartoons, murals, and all manner of graffiti. There are small hopper windows, but these admit little natural light, to the point where Wayne is concerned about Stewart and Roald's health and gives them a bottle of Vitamin D as a Christmas gift ("The Three Wise Men").
The basement is situated in town, as seen on the map he draws for F.A.K.U. operations ("Les Hiques"), and when Jonesy and Reilly lurk outside planning to trash the place in revenge for the rookie using meth ("A Fuss in the Back Bush"). What building it is the basement of is less clear. Roald mentions that Stewart lives with his mother, a statement which is "verifiable" ("Great Day for Thunder Bay"). It would seem logical that the basement is located in her house or apartment building, but Devon is able to evict Stewart from the premises when they come into conflict.
This is not your basement anymore. This is my basement now. And you are not welcome. — Devon