Here's an exhibition you'll enjoy because it's about what's under London, and that's very much your kind of thing. Very probably.
Under Ground London is the latest exhibition at the London Metropolitan Archives, and is up and running until October. The LMA is the capital's premier county record office, administered by the City of London and located in Islington. It opens weekdays only, except Fridays, but also the first Saturday of the month, which sorry you've just missed. It's primarily an archive so busy with staff and visitors heading for the reading room, but also free for anyone to wander inside and access the staircase to view the exhibition on the first floor landing. They've packed a lot in.
A quick scan of the subterranean categories displayed includes the obvious - sewers, railways, lost rivers - but also the less obvious - public conveniences, caves, conduits and burials. None of these can be done justice in the space provided but that's not the point, which is to showcase some of the relevant gems the LMA has in its A. Should an old document, photo, illustration or map pique your interest, you could always pop into the research room nextdoor and search for several more like it.
I lapped up plans for Southall's nuclear bunker, never used in anger, with air filters and single sex dormitories clearly marked. I queried the old wives' tale about wild hogs in the Hampstead sewers. I gasped at the intricate network of pits dug beneath Alliance Road in Plumstead. I loved Charles Pearson's unrealised plans for the first Underground railway station at one end of Smithfield Market. I stared for ages at the plans which showed precisely where the River Fleet flowed past buildings since replaced by Farringdon station. I was intrigued by the abandoned cobbled street supposedly hidden under Lilley & Skinner in Oxford Street. I watched the 1970s documentary snippet about Mail Rail with a nostalgic smirk. There was a fascinating nugget on every wall, usually several.
The free exhibition guide with colour cover (as only the City of London can provide) made for a scholarly takeaway summary. My congratulations to the curators for digging out such a densely packed and diverse collection relating to life under London. Half an hour should do it, sometime between now and the end of October.