But then two things occurred to me:
- This should apply to a lot more than just secret doors. Traps as well, of course, but also dungeon dressing, the layout of rooms, and even which rooms exist in the dungeon in the first place.
- Attaching this to a single named creator is way too obscure - it's unlikely that a single group of PCs will adventure in enough "Saul Stonehammer" dungeons to warrant learning those motifs and calling cards. But if the motifs are done by race, and especially if that lore is at least somewhat known and becomes available to (some) PCs - dwarves and artificers in particular, but perhaps others... well, that might be interesting.
Dwarves: The first and most obvious candidate, I can picture dwarves building lots of little way-stations and tombs on their escape from the Underdark. Features are likely to be strong defences, but also multiple exits, including well-hidden secret back doors.
Goblins: I envisage the goblins being a somewhat fallen race, given to cunning but not craft, at least in the modern age. But that suggests there may be all sorts of old goblin ruins out there, filled with crafty tricks, traps, and treasure for the daring adventurer.
Kobolds: The theme here is warrens, narrow winding passages, and lots and lots of traps. These are dangerous places, but they also hide all manner of arcane lore.
Humans, ancient: The people of the ancient world were masters of techniques and technologies far beyond their modern kin. Ancient human dungeons are old but they are well made, and they are places of wonder.
Humans, modern: By comparison, modern humans build dungeons that are plentiful but which are, comparitively speaking, shoddy construction.
Giants/Dragons: These dungeons are monuments to hubris - places built on a grand scale to show off the power of those constructing them. But they were also largely assembled by slave labour, which means that the work is not terribly well done, and leaves them prone to collapse or worse. Beware!
Wizards: Speaking of hubris, wizards have enough of it to demand their own category. The theme here is on strangeness - you might well find a staircase here that only goes up, or 'doors' that connect to wildly-separated places. Basically, in a wizard's construction all bets are off!
Unknown: The ancient world had at least one empire that is no longer recorded in history, and they left behind several ruins. Little is known about these builders, except that they made extensive use of a snake motif, and were great believers in strange angles and curves.
And that's where I am so far. Eight sub-groupings is more than enough (indeed, might be a few too many), but should give plenty of variety. There's more to be gained from this topic, but doing so would need more work than I'm ready to put in.