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Cold War bunkers, abandoned Tube stations, buried rivers, deep level shelters...London's concealed features are among its most intriguing. So, in age-old Londonist tradition, we've created a map to try and show what a hollow city this is.

And we need your help.

We've plotted the more obvious features - the Fleet River, Zone 1 ghost stations, the Kingsway telephone exchange, etc. But we know there's a lot more down there. Please use the comments to draw our attention to omissions. A few (flexible) rules...

(1) We only plot places that the general public cannot normally gain access to.
(2) Working Tube and train lines are not shown.
(3) Only spaces big enough to comfortably accommodate a person are included - ruling out some sewers and telecommunication ducts.
(4) A few other places we know about (e.g. River Tyburn) are not yet shown because we couldn't find accurate guides to their location or route.

We'll keep the map updated as people send in new information.