I love to look at Ordnance Survey maps: the iconic plans of the British countryside, which have served as faithful guides to generations of walkers. It's a form of geekdom I'm proud to admit to, and the nicest thing about this warm-and-fuzzy show was that it proved I'm not the only one. On the night I attended, the Dukebox was full of navigators of all ages – united by our readiness to laugh at jokes involving contours, and cheer at a shelf stacked with Landranger sheets.

Helen Wood's solo act has a beguilingly simple structure, and that's really all that it needs. Sometime last year, she went for a walk – joined by her apparently long-suffering husband and, needless to say, her dog. She plotted her route on (of course!) an OS Explorer map, and took entertaining selfies at key points along the way. Resisting all things digital, she displays the photos on a stack of old-fashioned flash-cards – and each stop also acts as a kind-of imaginary viewpoint, a paper-thin justification for a cartographic anecdote or two.

There's a lightweight moral waiting at the end of the journey, just enough to satisfy that part of your brain that wants there to be a purpose to it all. But really, this is a shameless miscellany, as varied and changeable as countryside Wood was walking through. Here, there's a poem, hilariously name-checking the features from an OS map's key; there, it's a series of comic character vignettes, delivering a surprisingly informative history of the Ordnance Survey itself. Some of my favourite stories were personal ones, explaining why Wood's so drawn to these pieces of folded paper… and although her memories are completely different to my own, they somehow still reminded me of my childhood.

Along the way there's plenty of good humour, and Wood quickly builds up an enviable rapport with her audience. Her chat is liberally sprinkled with OS-themed questions; there's no pressure to get involved, but there was never any shortage of people ready to shout out replies. There's a subtly conspiratorial feel to it all, the sense that we're all sharing a harmless but secret pleasure, and the best thing about it is that it has to be real. You wouldn't do a show this niche if you were making it up; the only explanation is that Wood realy is as lovably enthusiastic as she claims.

The humour's aimed squarely at a particular type of connoisseur and, if you don't know your Church With Tower from your Church With Spire Or Dome, it might not be the show for you. But if you think you might enjoy it, you're almost certainly right – so turn off that sat-nav and find your way down to the Dukebox. Rendezvous at 6:15pm; grid ref TQ299043.