Ruins of Thetra Mage College Lower Levels

Just enough dungeon to connect all the stairs slopes and trap doors from level 1 and outdoors. Numbered but not populated. C' connects the sloping passage from B14 with the trapdoor from B2, and the hidden staircase from B15.
D' connects the long staircase near B16 with the staircase from A4, and the open area off of B9. E is reached by a secret door in the trunk of the Tree in D3. Had intended to expand these levels as play on level B progressed. However the TPK on level A, followed by a lifetime ban on this dungeon from She-who-must-be-obeyed, rendered that effort moot.
P.S. for an interesting corollary of the problems this dungeon encountered read this review of Death Frost Doom .

Unfortunately, sometimes even the best sounding dungeons on paper do not click with the players in the field. This dungeon did teach me a lot about player-DM interaction. Most of my modern dungeons are a lot less scripted and adapted on-the-fly to suit the players motivations. Good for playing, bad for producing a module for publication and universal appeal.