Real World Inspiration for Dungeons

From time to time, Dragon magazine would feature articles about real world locations as inspirations for dungeons.  See for example issue #201 which included an article by Allen Varney ("Turkey's Underground Cities") about his trip to the cave cities of Turkey and some ideas for gleaning inspiration from that sort of setting.

I think that real world dungeons can be a good source of inspiration.  I would recommend visiting cave tours or historic mines in your area (or similar sites).  These trips can provide insight into how underground environments work.

Similarly if you have the chance to tour a historic castle or two, these can also provide insight and inspiration for dungeons in these cornerstone fantasy structures.