Earlier this week, Vincent Callebaut, the Belgium-born architect with fiercely eco-utopian leanings who previously introduced us to self-sustaining “farmscrapers” in China and a vertical agricultural hub in New York City that’s been described as a “locavore wet dream,” unleashed his latest vision upon the world: a floating city off of Rio de Janeiro where denizens — excuse, aquanauts — live, work and farm within jellyfish-inspired sub-aquatic hubs built with plastic sea trash using 3-D printing technology.

Callebaut’s concept is presented entirely in the form of a lengthy (and single-spaced!) letter penned by Oceane, a 15-year-old resident of said futuristic sea colony. The letter is dated Dec. 24, 2065.

While the whole thing is kooky as they come, this latest bit of fantasy-making from Callebaut also, in a way, encapsulates the year in design here on MNN: radical solutions — solutions largely but not always speculative, ranging from the eyebrow-raising to the completely improbable — posed in direct response to specific problems, from the dearth of bike parking in Amsterdam to rising sea levels across the globe.

In a year that was certainly without a deficit of flashy — and often ridiculous — architectural renderings, restraint was thrown clear out the window in favor of impossible idealism. It was a great year to be a dreamer, a starry-eyed do-gooder, an adaptive reuse-minded developer or a Russian oligarch with real estate concerns in London. It was a year that looked beyond the constraints of land-bound living — beneath the ground, in the sky and over (and under) the water. It was great year not to be afraid of heights. It was a year seemingly without rules.

Even if some of the more far-out projects that I featured this past year can easily be tucked away into the “never gonna happen" file, they do draw attention to pressing issues as if to say something, but maybe not this thing, needs to happen.

Below, you’ll find the biggest, boldest and most bananas architecture, urban design and civil engineering concepts introduced this year. Some may eventually be realized decades from now, some need a few years for advances in technology to catch up, some are already in-progress. I’ve listed them in descending order of plausibility.

Egg-shaped, off-grid hideaways, Slovakia

One part pint-sized trailer home, one part ovoid space pod (or as I put it back in May, an “inhabitable PedEgg”), the initial design renderings for this off-grid domicile that promise “dwelling with the spirit of freedom” were appropriately out of this world. Earlier this month, the 88-square-foot EcoCapsule officially became available for pre-order on planet Earth with a sticker price of €79,000 (about $85,600) and an anticipated release date of late 2016.

Ecocapsule, an off-grid, egg-shaped micro-retreat from Nice ArchitectsThe EcoCapsule. (Rendering: Nice Architects)

Underwater bicycle parking garages, Amsterdam

True, “underwater bicycle parking garage” has a distinctly utopian ring to it. But Amsterdam, a city that's home to a bajillion bikes and limited terrestrial real estate, really needs 'em. As I wrote back in March, “while a historic European city that's littered/plastered with chained bikes in certain areas makes for striking photography for out-of-towners, it also detracts from Amsterdam's singular beauty. Stashing away bike parking in less conspicuous but still convenient locations helps bring the focus back to the buildings, the parks and all the other things that make Amsterdam such a stunning place to live and visit.”

Bike parking in AmsterdamThere are so many bikes in Amsterdam. Where to put them? (Photo: Aiala Garcia/flickr)

Aging overpass transformed into floating arboretum, Seoul

If all goes as planned, the current Seoul Station Overpass, a crumbling two-lane roadway in the heart of South Korea’s capital city, will be reborn as most verdant stretch of reclaimed infrastructure this side of the High Line. Rotterdam-based MVRDV is behind the striking design that transforms a '70s-era overpass into a tree-studded floating public garden and pedestrian shortcut. Although not without some opposition, this government-supported plan could be open to the public as soon as 2017. Speedy!

A look at MVRDV's proposal for the Seoul SkygardenVisions of a verdant new path in Seoul. (Rendering: MVRDV)

WIld 'n' crazy footbridges, London

The first round of the Nine Elms to Pimlico Bridge Competition, a search for a “technically rigorous and beautiful” footbridge to span the River Thames, was lousy proposals that were fanciful, freaky and aggressively avant-garde. The British press, predictably, had a field day with some of them. In the end, it was one of the more restrained 74 submitted designs (not the one pictured below) that was ultimately shortlisted and then selected by the competition jury as the new £40 million pedestrian and cyclist span.

A design proposal in London's Nine Elms to Pimlico Bridge CompetitionOne of 74 submissions for the Nine Elms to Pimlico Bridge Competition. (Rendering: NEP Bridge Competition)

A dying suburban shopping mall reborn ... with the world's largest green roof

Shopping mall nostalgists avert your eyes. The undulating swath of green shown below was a dying 1970s shopping center in Cupertino, California. That is, until Uruguayan architect Rafael Viñoly came along and put it out of its misery. Blanketed with what’s billed as the world’s largest green roof — a 30-acre “integrated community park and nature preserve” complete with community farms, wildlife refuge and jogging trails — the $3 billion Hills at Vallco redevelopment project has to pass through more than a few bureaucratic hoops before becoming a reality.

A rendering of Cuptertino's new Hills at Vallco neighborhood designed by Rafael Viñoly Architects and OLIN.The 1970s-era shopping center may one day look like this. (Rendering: The Hills At Vallco)

Sports stadium-turned-urban surfing village, Perth, Australia

I've never surfed in my life, and I know little about the fascinating and technologically advanced artificial wave-making industry. Still, I'm kind of in smitten with the proposed repurposing of an old Aussie rules football stadium outside of Perth into a state-of-the-art man-made surfing lagoon that's ringed by housing. Local reaction, however, has been mixed, with some worrying about congestion and others questioning the need for an inland surfing facility when the actual ocean is a quick drive away.

Rendering of Subi Surf Park, an inland urban surf village proposed for suburban Perth, Australia. Repurposing gone wild in Perth. (Rendering: MJA Studio)

Luxury condo-spanning swimming pool in the sky, London

Soaring 115 feet above a massive mixed-use redevelopment project around London's old Battersea Power Station, this conceptual clear-bottomed swimming pool for the ultra-rich instantly spun the press into a tizzy. While thrilling to imagine, it is, in the end, obnoxious. And considering the woefully imbalanced state of housing in the British capital city, this luxury apartment amenity that "stems from the desire to the push the boundaries in the capability of construction and engineering" could happen. (After all the hubbub, it still appears in the development's marketing materials). Or maybe not — it's pretty insane. Whatever the case, don't count on being able to use it unless you happen to be BFFs with a visiting dignitary.

Sky Pool: A building-spanning, clear-bottomed swimming pool proposed for Embassy Gardens at Nine Elms, London.I see you down there. (Rendering: Ballymore)

A wind turbine that's also an observation wheel and an apartment complex, Rotterdam

I was never able to quite wrap my head around this one, an audacious project that serves as a distinctly Dutch contribution to the giant urban observation wheel trend. A wacky, wondrous tribute to the Netherlands' ages-old practice of harnessing the wind, the Dutch Windwheel isn't just a turbine reimagined as a fairground attraction. As I noted back in February, it's also "one part housing development, one part luxury hotel, one part renewable energy showcase and several parts unabashed tourist magnet." Basically, a shoo-in for Rotterdam, if they can make it work.

Dutch Wind WheelWhat else can it do? (Rendering: Dutch Windwheel Corporation)

3-D-printed floating dorms, Stockholm

From the always provocative futurists at Belatchew Labs, this offshore communal housing complex for 20-somethings taps into rapidly advancing 3-D printing technology. Called SwimCity, the Swedish National Board of Housing, Building and Planning-back concept — a "soggy new take on traditional urban infill projects," as I called it back in March — also incorporates emerging forms of renewable including wave and tide power. Bring your Speedo and a mini-fridge.

SwimCity, a conceptual floating housing development for StockholmWhat if you don't swim? (Rendering: Belatchew Labs)

A car-free housing development that's a little Ewokian, a little bit New Urbanist

So when can I move in?

OAS1S, a tree-inspired green housing concept from Dutch designer Raimond de HulluHope you like green. (Rendering: OAS1S)

Floating retractable ice rinks on the Thames, London

If the East River in New York City can get a floating swimming pool, why can't the Thames get lily pad-esque retractable ice rinks that aim to "return the winter spirit to the capital?" While no doubt improbable, there's a lot to like about this cold weather pipe dream. And just as fascinating as the design is the history: once upon a time when the Thames routinely froze-over, the tideway played host to not just ice skating but some seriously debauched-sounding public fetes.

NBBJ's Frost Flowers concept bring pop-up ice skating rinks to the normally not-frozen-over River Thames. A vision for retractable ice rinks on the Thames. (Rendering: NBBJ)

>Moving walkways to replace the circle line, London, England

From the same firm that plopped ice rinks onto the Thames, this three-lane moving walkway scheme that replaces trains along the perpetually packed circle line on the London Underground is a response to an urban design competition calling for "hypothetical but realistic proposals to make London a better place." While light on the realism (I can't stop picturing extras from "Logan's Run" toppling over like dominos), it's a fun idea to ponder particularly since it offers an an active alternative that's faster than taking the train.

A rendering of a proposed moving walkway that would replace trains on London's Circle Line. Miss the train? Just take the moving walkway. (Rendering: NBBJ)

Tornado-shaped weather museum, Tulsa, Oklahoma

Personally, I think erecting a tower designed to look like a massive funnel cloud in the middle of a tornado-prone region is incredibly bad mojo. But that's just me. Others have called the idea insensitive and tone-deaf. Proponents of the so-called Tulsa Tornado Tower — a tourist-snaring structure that would house a weather museum and a revolving restaurant that spins counter-clockwise, just like the real deal — see it as a playful yet potent potential Oklahoma landmark. Says museum consultant Kerry Joels: "Oklahomans are survivors. They’re tough, and they look at these things as a matter of life."

Tornado Tower, Tulsa OklahomaIs a funnel-cloud building a good idea in tornado country? (Rendering: Kinslow Keith & Todd)

A toll bridge made from upcycled aircraft carriers, Bremerton, Washington

When life gives you mothballed aircraft carriers why not make ... toll bridges? While it's highly unlikely that this congestion-alleviating transportation proposal in Puget Sound will ever fly for a variety of reasons (the Navy has already said no thank you and no way), I can't help but admire the creative reuse-minded gumption at play.

Retired navy aircraft carriers in Bremerton, Wash.Thinking big in Bremerton. (Photo: Clemens Vasters/flickr)

Times Square stuffed into a skyscraper, New York City

The eVolo Skyscraper Competition, an annual showcase of problem-solving vertical design proposals, never disappoints on the quixotic front. This year was no different with finalists that include a bonkers "Bio-Pyramid" for Egypt and a so-called "Shanty-Scraper" that provides housing to impoverished Indian fishermen. And then there's Times Squared, a tower-bound mini-city complete with beaches and a Redwood forest that rises 6,000 (!) feet above Manhattan.

TimesSquared-2Rendering: eVolo Magazine

3-D printed housing development, Mars

Although it was a big year for the Red Planet, the likelihood of this modular Martian housing concept — robot-built astronaut pied-à-terres, basically — in which regolith is harnessed as an indigenous building material, is decidedly a ways off. A long ways off. Still, it didn't stop Foster + Partners, a venerable firm that's no stranger to space exploration, from scoring second place in the 3-D Printed Habitat Challenge, a $2.25 million competition — “Solving the need for safe, secure and sustainable housing on Earth and beyond” — launched as part of NASA’s Centennial Challenges program.

Modular Martian dwelllings from Foster + PartnersOn Mars, we'll have to live somewhere. (Rendering Foster + Partners)

Liberty Bridge, New York/New Jersey

The only thing less immediately conceivable than parachuting robots onto the face of Mars to build huts out of dust is a mile-long footbridge that links Lower Manhattan with Jersey City. But hey, one can dream.

Liberty Bridge, a proposed Hudson River crossing for pedestrians and cyclists that would connect Jersey City and Manhattan.Why not connect Lower Manhattan with Jersey City? (Rendering: Liberty Bridge/Jeff Jordan Architects)

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.