This may be the single most useful tool you’ll find in the Internet: A wholly customizable Dungeon Generator. Just enter general dimension, denseness, even a % chance for secret or concealed doors, hit ENTER and -zoom- you’re there.
Notice the nice touch of the graphics? Like in the good ol‘ „D&D 1st edition“ days. Oh, and did I mention that the rooms are already randomly filled with monsters and include difficulty numbers for skill checks and all?