Theoretically any box can be a detox box as long as you stay in it long enough and don't bring any toxins in with you, but the Detox Box makes bold claims for its efficacy: apparently it can rid my body of heavy metals, improve my skin and relax my mind. So what is this magical machine?

Well, it's a sauna. Not just any sauna, mind - the Detox Box makes use of deep infrared rays, like a baby incubator, so it can operate at lower temperatures than a conventional sauna, while making you sweat more, the better to extract all those toxins. I will put aside for one moment the dubious notion of "detox", along with the claim that a special sauna will make mercury come out of my pores, because I want to go in the box.

Had I known that my destination, Totally Fitness, was not a spa or gym, but a showroom in central London, I might have been less keen. Sitting in a garden shed sweating like a pig is not something that should be done on a shop floor. Never mind - I jump in at 38C and watch the reading creep up to 50C.

It is strange to sweat so profusely without exercising or being extremely embarrassed, although I do blush a little when customers come in looking for boxing gloves. Because it's so much cooler than a standard sauna, the air doesn't scorch the inside of your nose. Nevertheless, after 10 minutes I am drenched and dripping. I've drunk a litre of water, but may as well have just poured it straight on to the floor. Yet it's comfortable, even rather pleasant. I could stay here all day. I want to go to the 70C maximum - I know I can handle it - but the sales guy won't let me.

Afterwards I feel pleasantly wiped out. Deep infrared rays are nothing new - they are commonly found in sunlight - but at this time of year I'll take them where I can get them. When I go to change I have to walk glistening in sodden shorts, through an office full of people on the phone. That's when I start sweating out lead.

· Next week: Lucy Mangan on her bike