They already peak interest when it comes to guided walks but now London's old unused tube tunnels have attracted some different attention - from companies who have been invited to bid to transform them.
TFL has offered up the disused tube stops and horse tunnels under London to see what ideas other companies may have for them. The public body owns 750 of the tunnels and is looking to transform the portfolio of assets. We wonder if this will take out ticket prices down or up?
TFL is currently deciding wether to let construction firms to bid for just one site to kick-start the project, or a collection of the spaces hidden.
It does sound pretty exciting - very demolition man but with less rat burgers.
Deals are already in place for some tunnels. Those below Clapham North are now home to a herb farm, and the organisation has signed a deal with Waitrose to run a service where customers pick up goods from lockers at Chalfont & Latimer, on the Metropolitan line.
What would you like to see in the tunnels?