I am reading a novel called 'Tunnels', about a boy and his dad who dig into forgotten tubes and chambers under London.

Sounds facinating.

There've been some excellent stories and films based on these old abandoned stations. One in particular, from the 1960s, I remember starred Donald Pleasance and was based on the premise that a group of workers (male & female) had become walled in, by mistake during 19th century construction. They had existed on rats and drips of rainwater, had adapted to the darkness and, naturally, had procreated. Their numbers had outstripped the food supply (rats) so they were preying on unsuspecting passengers waiting alone at night on the subway platforms. Various body parts, half eaten, turning up on the tracks alerted the police to what was happening. An effectively scary movie, with an at least semi-believable plot.

Good story, digital!