These designs go beyond bizarre, slip past strange and go straight to spectacular. From hotels in the air and underground houses to cave dwellings and floating homes, these works challenge even the basic assumptions that architecture for living in requires footings, walls or even roofs.

Perfect for a private overnight stay with an amazing view, converted cranes are conceived of as rooms in the sky – lofted bedrooms that take you up high at the push of a button, then back down the next day.

Aristide Antonas is as much an artist as he is a designer, with multi-media works of collage, montage, drawing and sculpture that are compelling artworks as well as design ideas – like cliff-side homes made to look like caves or culverts or walled-off spaces with the trappings of a normal dwelling, except the all-critical roof on top of it.

Along the same lines: a modern-day watchtower with some walls and roofs, but that is mostly open to the air and views around it with only minimal protection from wind and rain – a contemporary modernist design of simple planes and smooth surfaces that lacks even the details of glass or doors.

Or consider this catamaran: a single-room space tucked in a boring-looking shell yet perfect for its nautical purpose as a floating home with a roof-top deck above and sleeping, living and eating spaces below.

He also works at urban-design scales as well, like this sideways skyscraper idea – a design to turn London Bridge into a occupied series of linear flats, passageways and stores to support a sort of city-within-the-city.