ERRRRR what? A super cool idea! Transport for London has created a map that shows you which tube lines are underground (apparently more than half are not!) and if so where on the line they are. The map takes a second to get to grips with but the idea is that for those who find the whole under-the-ground bit of the underground challenging you can plan your routes to avoid these areas.
I found a link to this on The Mighty but once i checked it out on the TFL website i found a whole list of cool maps to help with a variety of issues including wheelchair access and toilet facilities which for someone with IBS is actually really helpful. To access the TFL page including a link to the ‘stress free map’ (Tube map showing tunnels) and all other kinds of useful maps click here.