Really large dungeons: scan and print
Rob posted about drawing large dungeons on large sheets of graph paper. I thought I’d mention that most Kinko’s (now FedEx Office) can scan, print, and copy arbitrarily long sheets of paper up to 36 inches wide. Scanning is $1 per square foot, and printing is 75¢ per square foot. That’s for black & white; color is probably a lot more expensive. You could also use oversize printing to do things like draw several super-detailed maps on 4x4 grid paper, scan, digitally combine, reduce, and print them on 36” wide paper for a huge map with minute detail. Or draw your map on 24” x 36” paper, scan it, and print it at 8.5” x 11” or whatever. Searching Amazon for grid vellum 36” or grid vellum 24” gives several options for large original drawings.