The Way We Live Now: Down under

You could be Going Underground any time soon. It's what people do now, particularly if they've got tall thin old terrace houses. With a terrace you obviously can't build out sideways, you'll probably be restricted about what you can stick on the back – especially if like big city-central terraces there's no garden. And the planners won't want you putting another story on top, messing up the historic roofline. It's all so much easier in Guildford and Alderley Edge.

So you go burrowing around; stealing space from the moles. You think of newer grander or more tech-y things to do with your basement (now universally re-branded as 'lower ground floor'). Instead of the traditional kitchen / dining room combination you could go for all those things modern plutocrats need – a home cinema, a gym, or a swimming pool, You think about ways to extend the basement by digging out under your scrap of yard. You think about poshing up the whole area by digging the entire floor down a couple of feet. Could a cellar become a suite? And what if you've got under-street cellars facing back into you basement windows? So what if they're low and damp, dark and mouldy-smelling, they can fix all that now. In Big Cities with old basemented houses where space is tight there are specialist firms who package it all for you. The design, the planning permission, the digging and 'tanking' and finishing and piping up and the rest of it to make something like what they show in their brochures. It costs twice what you think and takes ages longer but if you can magic up a new bathroom or a laundry, a glamorous wine cellar – or, better still, some bearable bedrooms – then it's paid for itself.

Underground design suits applications that don't need natural light – home cinemas need velvety dark, wine cellars should feel enclosed – or where the cost and cleverness of the fitting out compensate for everything, nightclub style.

Underground rooms have a look. Arches and pillars, bare vaulted brick and all the other tricks of old crypts and dungeons. It all looks good when it's scraped modern. You can compensate for the lack of light – make everything pale and reflective – you can even fake it with false windows with an electric glow from behind opaque glass.

Or you can make it darker still, disco it up with dark shiny reflective surfaces, banish the mould under every kind of cladding, exorcise the spirits with glowing , winking tech – the recording studio look. Put lights in the floors and the stair treads. Eliminate anything organic in favour of the highly unnatural. Hard floors in smooth stones so precise they look like plastic will show the earth who's boss.

This underground bedroom barely needs to try. The vaulting does most of it, the bare brick does the rest. This isn't a place for anything too fresh and perky. Instead it's a bit Regines and a bit North African, with churchy overtones. The colours go from dark brown to cream floor, via mango walls. But the frosted glass doors with their minimal detailing (to a bathroom?, a dressing room?) are clearly modern, like the overscaled brown headboard or the shiny brown bedcover. Somebody's thought all this through. The furnishing's restrained exotic, with what looks like a Euro eye. The domed coffer to the left looks vaguely Moorish, like the arched mirror above. The dark cupboard beyond looks like church furnishing. And you strongly suspect that the plates above the bed – all black and deep clay red – feature the sort of beastliness you might see on an early Greek vase.