It might be most famous for its lotions and potions, but the treatments offered at the Lush Spa are also the bomb.

The first weeks back at work after Christmas are consistently rubbish. You have to sit up properly instead of sleepily reclining. You've sworn to eat healthily, while a landfill's worth of chocolate protrudes out of every available cupboard. You're having trouble adjusting to wearing a bra again, and don't even get me started on the amount of showering required. Utter rubbish.

That's why I was pee-my-pants excited to be visiting the Lush Spa on Edinburgh's Princes Street for its signature treatment Synaesthesia. Princes Street in January isn't exactly renowned for its tranquillity, so after a bargain-hunter slalom the serenity of the spa is a (pleasant) shock to the system.

Located underneath the Lush store, the spa is designed to replicate founders Mark and Mo Constantine's kitchen, so expect to be completely charmed by the quirky mismatched crockery and handpicked posies of flowers. My spa therapist Rhoda talks me through the treatment - it's a full body massage with different elements to stimulate the various senses.

Synaesthesia is a neurological condition where two or more senses merge, for example, sounds having a colour or shapes having smells. Notable synesthetes include artists David Hockney and Wassily Kandinsky, as well as Pharrell - a massive hat must smell like a good idea - so a side effect certainly seems to be creativity. Mark Constantine is said to suffer from scent-shape synaesthesia and this was the motivation to create a treatment that stimulates scent, sound, touch and taste.

To start, I picked a word from a massive chalkboard in 'the kitchen'. Not surprisingly, my festive-bloated face was instantly drawn to 'esteem', of which I had a massive potato-shaped dent in my own. The word choice decides what type of massage bar is picked from of the row of mason jars crammed with goodies.

Then, I walked over to a shelf covered with different bottles of varied sizes and colours. I browsed the labels while I made my next selection. It seems the treatment can target a number of concerns, and 'forgiveness' and 'acceptance' seemed like popular choices. I opted for 'go do' because who doesn't want to beat the inevitable January slump?

Through in the purple-lit treatment room, Rhoda had tee'd up some beakers that were bubbling away with the 'go do' scent, with white steam cascading over the glass and filling the room with a gorgeous, heady smell.

I was given a bell and told to underdress to my pants and hop under the cosy blankets on the bed, and when I was ready to ring the bell. It's a simple but brilliant idea and it's surprising more spas don't do this. You don't have to do the Supermarket-Sweep-speed-strip that always happens at this point, and you don't have to awkwardly stare at the ceiling once you're done (while you silently curse yourself for hastily ripping your tights off). I did not pretend I was a showgirl and ring the bell at the end of my dance.

The lovely Rhoda cleansed my feet and moisturised them, which always feels like heaven, unless you're one of those weirdos that can't bear your feet being touched (FYI: I find you guys even worse than foot fetishists - get involved!). Even remembering I'd forgotten to shave my 'winter coat' legs couldn't quell the relaxation that coursed through my body with every pummel.

One of the most interesting parts of any treatment at the Lush Spa is the unique, individual soundtrack. Devised to complement what's happening in the treatment room and take you on a 'musical journey', it's a refreshing change from the standard spa set. Familiar, comforting sounds like birdsong and even the noise of cars driving past in the countryside all tap into your subconscious childhood memories and heighten your relaxation. Accompanying the chirping is a 52-piece orchestra, an impressive feat that ties in perfectly with the multi-sensory approach of the treatment and the holistic ethos of the spa.

It's no hyperbole to say Lush employees and fans are cult-like in their devotion, myself included. With a happiness that's normally reserved for medicated Americans, nothing is too much trouble for everyone that works there. And like Fran Drescher's laugh, it's completely infectious.

Back in the cottage-style kitchen, I jokingly proposed to Rhoda while she made me a cup of 'esteem'-specific herbal tea, and once I'd been politely rebuffed I said my goodbyes. But I didn't go away empty-handed - after Synaesthesia you're given a massage bar and bubble bar scented with the same oils used in your treatment.

I've been for a different treatment before and the spa therapist actually walked me round the shop floor picking the products for the treatments and explaining the benefits of the ingredients. I'm always a little awkward about the 'upsell' of the premium products available in spas but at Lush this couldn't be further from the truth - not only are the products great value but it's definitely not a 'hard sell', more a handy demonstration of how you can recreate the treatment at home with willing participants (did someone say pals, prosecco and PMSL?).

It wasn't my first visit and definitely won't be my last - in the meantime I'll be swinging by to pick up a Unicorn Horn Bubble Bar because it looks prettier than Harry Styles wearing a bonnet and singing 'The Good Ship Lollipop'.

Treatments start from £40, while Synaesthesia costs £125 for 80 minutes. Lush Spa Edinburgh, 0131 225 4688,