Dom Joly: If I do find a monster, no one will believe me

Brazzaville is quite an extraordinary place. It sits on the mighty river Congo, a vast expanse of muddy water dotted with dug-out canoes carrying sure-footed fishermen.

On the opposing bank is Kinshasa, a monster of a city compared with Brazzaville – it has 12 million inhabitants, as opposed to Brazzaville's modest one million. Every destination loves to have "traveller facts" about itself. The Congo is no different.

Everyone here tells you that nowhere else in the world do two capital cities sit within sight of each other on opposing sides of a river. This is a quite specific boast considering that Rome and the Vatican City traditionally hold the "two capitals closest together" crown.

A more interesting fact to me is that Brazzaville was the capital of "Free France" during the Second World War. General De Gaulle came here and declared it as such.

There is a very French feel to the architecture of the old "European Quarter" in the centre of the city, it reminds me a little of Phnom Penh. Not that there is much left: ugly new glass buildings are sprouting and the short civil war in the late Nineties laid waste to the city. There are still plenty of bullet holes and shell marks from the conflict.

Curiously, the city is almost entirely run by Lebanese. There are loads of Lebanese restaurants and even my hotel makes a mean fattoush. The Lebanese, descendants of the Phoenicians, are fabulous merchants, but to leave war-torn Beirut in search of quieter fields and to end up in the Congo is not necessarily a successful move.

My hotel restaurant is full of Russian businessmen and the Brazzaville ladies who lunch. The Russians all drink beer way too early in the day and smoke as if it was going out of fashion.

Every three hours or so, a couple of Congolese will come in and they will have long, shifty-looking conversations in the corner of the restaurant before returning to their beer and cigarettes. It's all very reminiscent of the Cold War, although the lunching ladies – bored wives of diplomats and businessmen – don't seem to notice or care about the intrigue around them. They drink white wine and are all on laptops showing each other clips of things with the volume on a little too loud.

One man, a Congolese, sits alone in the corner drinking vats of strong coffee. He has a mobile phone that is very loud but he never answers it. Every three or four minutes a sinister, tinny whisper blares out from it: "Boss, you have a text message...", but he never even looks at it, just downs another coffee and stares into inner space.

I am now leaving the relative civilisation of the capital to fly north over the equator and into the unknown. I discovered today that my guide, Jean-Pierre, has never been to the swampy forest area that we're going to. This was not exactly reassuring, but that's Africa for you – it's never the most reassuring of destinations.

My goal is to try to find the mokele-mbembe, a dinosaur-like creature that has been harassing pygmies in the area for the past 200 years. Who knows what we will discover? But then, even if I do happen to come across it, nobody will ever believe me anyway.

This is an adventure, pure and simple – the biggest adventure of my life so far, and I can't wait.