The idea being you post a topic you wish to know more about, and someone (hopefully) volunteers to write a guide on the topic and post it. The catch being that you should really be nice and give as you take..
We have a lot of knowledge on this forum and it would be a shame to waste it. So this is probably a good way of maximizing the sharing of information.
I'll kick it off by OFFERING a guide, not requesting it...
Topic: (Urbex) Sourcing Tunnel Maps + Overlaying with Aerial Photography
Summary: This would be a pretty specific guide so I thought I'd just check to see if anyone is interested first. It would start off talking about how you may be able to find tunnels (looking for air shafts, physical terrain features, weird manholes etc), how you could be able to source a map for the tunnels (Freedom Of Information, Official Archives, Local History sources etc), then studying the aerial photography of a physical area and matching them to likely tunnel locations.
It then goes into explain how using open source software (the GIMP) you can scale both the aerial photography and the tunnel map to a specific size, modify the tunnel map to a degree, then overlap them using layers and plot out likely access routes as well as define where they run under.
The reason for this guide would be as I am currently having to do it for a set of "lost" (well, newly secured and access points capped) tunnels a few towns over for me, and I hope to visit them this week.