|Art is always a good thing to include on hallways|
& make it about an upcoming room
There is a nice blog post here that I discovered in KNOCK! Vol. 1 about not making corridors featureless expanses. This matching with my own philosophy about not fighting in "white rooms" that are 30' x 30'. Or trying to create actionable empty rooms.
From the post:
Almost every time the players turn a corner something interesting should happen. This doesn't have to be a fight, just something interesting. Dungeons should not only be places of danger, but places of wonder.
The below list is just something I have been thinking about while keying a ~50 room dungeon I drew by hand using 2d6, a random roller, and graph paper. But I do want to liven up some of the hallways: (1) so they are interesting, but (2) so they might provide a reason to be carrying 50' of rope with a grappling hook or having party thieves.
Nothing super inventive here, but helps to keep me honest about the inclusion of things. I'll maybe try to do a Dreamland's version later.
For every hallway 60'+ roll 1d20 on the table below is what is going to trouble the players:
01 | Ceiling is covered in green slime (1-3) or floor is covered in brown mold (4-6)
02 | The glint of coins can be seen floating in mid-air (1-3 whatever PCs think it is, it's NOT a gelatinous cube; 4-6 whatever PCs think it is, it IS a gelatinous cube)
03 | The maw of the earth has opened up a 30' gap
04 | Pit trap (1-3) or Pit trap with rusted spikes (4-6, save vs Poison)
05 | Grave Wind- torches are automatically blown out (can't light in the hallway)
06 | Filled with giant crystals; thieves & halflings hide easily; dwarves want to mine it (save vs. Paralysis)
07 | Caved in (1-3 can't be cleared; 4-6 slowly crawled through 1 by 1)
08 | Alter is built into the wall (1 lawful 2-3 elemental 4-5 neutral 6 chaotic)
09 | Magic sconces light with a mysterious green flame all chaotic creatures turn invisible
10 | It is flooded to the (1-3) knees (4-5) waist (6) chest
11 | A small fountain (1-4 brackish water; 5 clean water; 6 potion)
12 | Sound echos really well (roll an additional encounter check)
13+ Unique tile patterns (helps provide a landmark for navigation)
Again super quick with stuff I was thinking about while folding laundry. Some of these options might be covered in room stocking, but maybe you'll be inspired by a few. And if so, add them in the comments!