The other thing I should be clear about is that the tables are deliberately written to be moderately system agnostic. When necessary I'll refer you to the rules of the specific game you're playing - rather than trying to describe an already existing sub-system. Not that I won't detail new sub-systems when it's appropriate.
Whats Blocking the Corridor? (1d12)
- Giant spiderwebs. Follow the rules for a Web spell as appropriate.
- A partial cave-in has filled the path with stone or dirt, determined by the referee. 10' sections of dirt take 1 hour to clear a pathway with shovels or 3 hours without shovels; sections of rock take 3 hours.
- The corridor is filled with refuse from elsewhere in the dungeon to the point where it is impassable. The referee should roll 1d6 to determine number of turns required to work through it. Each turn there is a 25% chance of encountering vermin (referee's choice).
- Rocks and boulders fill the hallway. It takes 3 hours to clear a 10' section.
- A magical wall blocks the way (referee's choice of any wall spell).
- The pathway is blocked by an iron portcullis, rusted shut. Refer to the rules for bending bars and/or lifting gates; a spell such as Knock will also open this.
- The entire corridor is filled with a gelatin-like substance. There is a 25% chance that it is acidic and causes 1d2 hp damage per round when characters walk through it.
- A wooden barricade has been erected. Each 10' section of hallway takes 3 turns to hack through if the party has axes; otherwise it takes a full hour.
- There is a curtain lining the entire width of the hallway. Naturally there are opponents appropriate to the dungeon level waiting in ambush on the other side.
- A mountain of skulls, meticulously stacked into a pyramid.
- The remains of some corridor-width monster such as a purple worm fill the hallway. It takes 1 hour to clear each 10' section, and the stench is awful.
- A red dragon (age category = dungeon level). Roll for initiative.