D&D 5E Giant Boulder vs. Immovable Rod

[Al'Kelhar]

...
Oh, oh, wait! Here's what you do...

Get yourself a big honkin' wedge of really stout oak, possibly bound in iron bands if you can manage it. Set it in the center of the corridor. Place the immovable rod against the downhill side of the wedge, and activate it. Yes, there will be more than enough force to deactivate the rod, but not before that rolling ball - that is traditionally only just big enough to fit in the corridor - will have tried to at least a bit roll up the incline, gotten several inches of wood under it, and wedged itself solidly in the corridor, unable to roll down.

"10' pole?"
"Check!"
"50' hemp rope?"
"Check!"
"Hooded lantern, flasks of oil, and some more flasks of oil?
"Check!
"Friggin' great big wooden doorstop?
"Ch.. wait, what?"

 

[Paul Farquhar]

If you somehow run over the SMALLEST THING (like, not exaggerating, a penny or computer screw) while moving that pallet jack the entire thing is IMMOBILIZED. No amount of brute force will get that 1500 pounds of servers up and over that penny. Its so ridiculous, but its true.

Added to that, such a heavy rock would likely crumble under it's own weight, and quickly stop being a sphere, bringing it to a grinding halt. The difficulty isn't stopping such an object, it is keeping it moving.

A steel sphere would be more practical if you wanted it heavier, brass even better.

 

[Paul Farquhar]

Or, you make the rock a cylinder...

A cylinder wouldn't be as likely to crumble as a sphere, but if it went even a tiny bit out of alignment it would wedge firmly against the sides of the passage.

 

[JiffyPopTart]

Can't resist anymore!

How I picture this giant ball trap.

 

[MarkB]

A cylinder wouldn't be as likely to crumble as a sphere, but if it went even a tiny bit out of alignment it would wedge firmly against the sides of the passage.

You'd just need to add a raised curb to the sides of the corridor to act as a channel and keep it aligned.

 

[Umbran]

A cylinder wouldn't be as likely to crumble as a sphere, but if it went even a tiny bit out of alignment it would wedge firmly against the sides of the passage.

Look, dude, if you are going to go through the trouble of managing a single 300,000 pound rock for the purpose of squishing people, you can manage this.

What is the point of going through the work of that rock, and leaving huge gaping holes a halfling could just walk through?!?!

 

[Imaculata]

What is the point of going through the work of that rock, and leaving huge gaping holes a halfling could just walk through?!?!

Maybe I've been designing my dungeons all wrong. What was I thinking adding all those secret passages, treasures and easily escapable traps?! From now on all my dungeons will be hopeless rewardless death traps.

 

[Umbran]

Maybe I've been designing my dungeons all wrong. What was I thinking adding all those secret passages, treasures and easily escapable traps?! From now on all my dungeons will be hopeless rewardless death traps.

You miss the point - scaling the boulder up to that grandiose size is what makes it escapable, and thus foolish. Adding the size makes it a worse trap, not a better one.

 

[Oldtimer]

This makes me think about the rolling boulder trap I had in a dungeon (used as a convention competion event) some forty years ago. The sloping corridor ended with a false door and touching it released the boulder. Almost all players realized the obvious way to avoid being crushed (round boulder in a square cross section corridor), but one group actually panicked and rolled repeated Open Door rolls (those where a thing in those days) until the boulder crushed their characters.
Oh, happy days.

 

[Eltab]

Maybe I've been designing my dungeons all wrong. What was I thinking adding all those secret passages, treasures and easily escapable traps?! From now on all my dungeons will be hopeless rewardless death traps.

The firm of Acererak & Grimtooth, Architects, invites you on a tour of their demo-dungeon.