My cousin Jeremy calls them doorbell bars. They are the venues that you could walk past on innumerable occasions without having any inkling that they are even there. Until this month, Bristol had three of these bars: Hausbar, Hyde & Co and Whitelock & Grace. We now have a fourth, the Milk Thistle, and although it is in the most central location, it is also the most secretive and exclusive yet.

It just so happened that Jeremy was visiting Bristol on Saturday night from his home in Cardiff, a perfect excuse therefore to ring the doorbell of the Milk Thistle for the first time.

In order to do this, we had to walk past the drinkers outside the White Lion next door. I don’t know what they must think of the building beside their local now back in use after years of lying empty. I don’t know why they think people are entering the building next door. I didn’t know what to expect until the door was opened for us.

And without wanting to spoil the surprise, I won’t give too much away. Apart from to say that what has been created here is breathtaking. To paraphrase Bill Bryson when he described Durham in Notes from a Small Island, “If you have never been to the Milk Thistle, go there at once. Take my car. It’s wonderful.”

The Milk Thistle has been created by the same people as Hyde & Co, and the small touches that make that bar such a delight are all here, but now spread out over four floors with a different feel to each. A basement vault is not yet open but there are plans for it to become a wine cellar and private tasting room.

There are Victorian curiosities on the ground floor replete with antlers and a stuffed fox wearing a bow tie, a more funky modern outlook on the top floor that can be hired for private functions, with the wood-panelled lounge on the middle floor aiming to be the preserve of club members willing to pay an annual fee for exclusive offers and preferential treatment.

Cocktails are the stock in trade of the Milk Thistle. Peruse the menu found within antique hardback books, but don’t stop at the cocktails as the bottled beer menu is as extensive as any I have found in Bristol. There is a variety of Luscombe loveliness if you’re on the soft drinks, but why ever for? One benefit of membership is a complimentary taxi service to the bar from a one-mile radius and reduced rates home at the end of the evening.

I was last in Quay Head House, where the Milk Thistle now calls home, in January last year for the fabulous pop-up restaurant Cloak & Dinner in what was then still a squat with huge bolts on the heavy door.

The late-nineteenth building used to be the offices of the trustees of Bristol Charities, the organisation founded and funded by wealthy benefactors to build almshouses for the city’s poor and destitute. Bristol Charities left Quay Head House in 1938 but the organisation still exists today. A glimpse of its past can be seen by the crests of wealthy merchants, including Edward Colston, on the frontage overlooking the centre.

Bristol’s fourth doorbell bar shares many similarities with its forebears, but the Milk Thistle is like nothing else you will find in the city. It is a unique experience, magical and mysterious. Ring that doorbell and discover its delights for yourself.

The Milk Thistle, Quay Head House, Colston Avenue, Bristol. 0117 929 4429.

www.milkthistlebristol.com