The Eighth Wonder of the World. As if the modest title isn’t enough of a build up, there’s the structure itself: the Thames Tunnel Shaft. You don’t expect to find a wonder tucked away in a nook somewhere by the undiscovered part of the river. You don’t expect the wonder to be a smidge unsightly from the outside (masked by a crowning and beautiful herb garden), and on the inside for that matter. Nor do you expect a wonder to play host to so much jeopardy upon entry (unless you’ve tried to climb a pyramid). There’s nothing natural about this wonder. It is a feat of intricate engineering by two minds colliding to catalyse genius: those of Marc Brunel (Peter Harding) and his son Isambard Kingdom Brunel (Ben Eagle), who engineered the first ever underwater tunnel (one of many firsts for Isambard Kingdom). The Brunels and their tunnel are a tough act for one play, lasting under an hour, to live up to.

As it turns out The Eighth Wonder of the World isn’t living up to anything. The play becomes a part of its surroundings, and is soaked in the history around it. Simply the effort it takes to enter the building and find your seat is theatre in itself: rustic and immersive. You are challenged to clamber down onto slender edges, before bending double (even at the tender height of almost 5ft) to make your way through a passageway and onto a precarious-looking scaffold staircase – unable to open your eyes until you reach the bottom, where you find the wonder. The tunnel shaft, having withstood generations and remained iconic, stands strong – iconic and damp – the harsh, industrial concrete made delicate by the flickering of candles. Festooned with Union Jack bunting, it is a reminder of how proud we should be of the Brunel legacy. Slap-bang in the middle of the shaft is a table, over which the Brunels must iron out their difference in the pursuit of their shared goal.

It’s 1827 and things haven’t been going all that well for the tunnel’s progress. A series of floods has caused physical damage to the construction, psychological damage to the morale of the workers and a vortex to throw the money down. All the money. Marc has been confined to his sick bed and the 21-year-old Isambard Kingdom, not quite a man though too smart to be a boy, has born the brunt of it alone. He opts to host a banquet, to show potential and existing investors his passion, skill and determination, reselling what is already there and exhibiting exactly what he is capable of. To pull this off, though, he needs tactics and techniques, the like of which he is yet to learn. An hour before the banquet is about to commence, his arrogant, fist-leading father pays an unexpected visit.

It’s a visit that humanises these figureheads of history, as they tread the same cycle we all encounter: balancing respect with knowledge, status, right and wrong; brawling like parent and child, quickly accepting, moving on and building a plan together. Nick Harrison’s script is natural and recognisable, though some of the language is notably modern. Harding’s Marc is self-assured and becomes more so as his reputation and authority is put under question. There is an underlying sense that his aggression is intended to push his son into brilliance. Eagle makes that son entirely controlled, patient and earnest. His intelligence prevails into thoughtfulness and the ability to take in everything before reacting rashly. He is as logical as he is likeable.

The only dislikeable element of The Eighth Wonder of the World is that it isn’t quite enough. It doesn’t fill the huge room that it is the nucleus of. There is not enough of a story to hold up the legacy it represents and the building we are watching it in. The play fizzles out, while the candles still burn to show its wonder.

The Eighth Wonder of the World is playing at the Thames Tunnel Shaft until 14 June. For more information and tickets, see the Brunel Museum website.