Fenced off or set back from streets and sidewalks and often raised on platforms as well, civic monuments are oddly ideal candidates for concealing a peculiar secondary function: the ventilation of subterranean spaces, from sewage systems to subway tunnels.

In Sydney, Australia, the Hyde Park Obelisk was built precisely for this purpose back in 1857. Modeled on Cleopatra’s Needle located on the banks of London’s River Thames, the 60-foot-tall tower was designed to allow noxious gases to escape upward from the sewers below. Today, the monument remains in place, but vents the city’s somewhat-less-smelly stormwater system instead.

Meanwhile, in Nuremberg, Germany, a controversial set of statues depicting the trials of married life was commissioned specifically to disguise the subway exhaust port located on the site.

The Ehekarussell (roughly translated: marriage-go-round) is critiqued not because of noxious fumes, but for featuring a sequence of scenes through its statuary: a young happy couple turning older and angrier before one spouse slays the other.

Another approach that appears in many cities is more architectural, though no less monumental, using anything from small fake shell houses to huge multistory buildings as giant exhaust conduits.

In Burnaby, British Columbia, a boxy little house serves both to vent subway fumes but also acts as a mid-tunnel escape route for emergencies. Many of these structures not only act as exhaust pipes, but also contain bacterium-based odour removal plants so as to spew somewhat less obnoxious gasses.

The Callahan Tunnel ventilation building in Boston is a relatively less-camouflaged and more-imposing affair built of bricks with vents where one would ordinarily expect to see windows. Many other American cities have similarly larger exhaust buildings, including New York City, where they vent infrastructure including the Holland Tunnel.

Below the streets of Hobart, Tasmania’s capital and most populated city, lie a network of centuries-old runoff tunnels that are slowly being turned into the backdrop for a growing body of collaborative (and sometimes creepy) art.

Urbexography (previously featured in a tale of Grimm Abandonments) has gone underground this time to capture the current state of the tunnel system and the strangely fascinating works that populate it at the present time.

One series in particular may be best avoided after dark: an array of plaster-cast doll heads, a tribute to catacombs lined with human skulls found elsewhere in the world.

Artist Shaun McGowan is behind much of the work. “I’d love to keep doing this project for years to come,” he told The Mercury. “It’s the opposite of gallery and studio work. There’s no barrier around it saying that other people can’t contribute or break it or do whatever they like. I love that collaborative nature.”

Remarkably, many of his interventions have so far remained intact, drawing tourists and thrill seekers by day and night to these once-forgotten waterways. McGowan does not expect any particular piece to last, however, and accepts that change is inevitable and the place will always be a series of works in progress. Meanwhile, see more photographs of this amazing and evolving set of spaces on Facebook.

The latest in a long line of city-centric upcycling projects, this modular couch turns the ultimate in untouchable urban infrastructure into a chic industrial work of furniture.

Carlo Sampietro created the Cloche Sofa after seeing a section of sewage pipe abandoned by a construction site, its spot being fit for replacement with a new set of tubes.

He then fitted the ends with stabilizing structural circles and plasma-cut sections for seats, welding them back into place, hinging them and creating two locked positions (open and closed). Various configurations can be achieved by opening and closing sections to create a pair of chairs, a love seat or a full sofa.

This is far from the first time that Sampietro has reworked urban elements into new forms – his Cloche Chairs turned safety barrels from “symbols of caution into objects of comfort.”

Some of his pieces draw on the visual language of familiar street objects, but interpret them in new ways, like this police barrier table constructed from walnut, steel, resin and using LEDs (which light up through its lettering below).

More about the sofa from the artist: “It represents landscape evolution that dismantles established structural standards and elements of construction materials, and repurposes a found material into sophisticated design, reshaping a common object into a meaningful amalgam. This piece harnesses objects that outlived their original uses, were discarded, reclaimed and renovated. The evolution of this landscape design could be achieved by taking in consideration other material such as concrete, stainless steel, wood or marble, all cylindrical forms present in existing construction materials or natural environment. The tube shape is accented by LED side panels and the conic footing. This renders the object’s hybrid functionality almost invisible, unnoticeable at the first glance.”