Fitting through is not moving at the usual cost
In the 2024 rules, a narrow opening sized for a creature one size smaller counts as Difficult Terrain. For a Large creature, dragging its piece across the drawing is not enough: establish the passage space and calculate the movement cost along the route.
The Difficult Terrain entry in the official 2024 glossary includes that opening and charges one extra foot of movement per foot travelled. This guide does not import attack or saving-throw penalties from another edition’s rule.
A Large creature and a Medium-sized passage
Authored table example: a Large creature must cross an opening the DM has defined as sized for a Medium creature. The narrow section is ten feet long. Without another rule changing the calculation, travelling those ten feet costs twenty feet of movement.
These are separate measurements: width explains why the passage is narrow for that creature; ten feet of length determines how far it travels inside. A thickly drawn doorway establishes neither measurement on its own.
If movement was spent before reaching it, add that expenditure to the passage cost. Twenty feet of cost does not mean twenty feet travelled. This example does not decide whether the creature fits an opening two sizes smaller or resolve geometry the map never defined: clarify it at the table before moving.
Prepare the decision in DMGrid
DMGrid provides a tactical board, distance ruler, pieces, turn order and session notes. Use them to present the map and retain the human ruling. This guide does not announce automatic narrow-opening detection.
Before the scene, check the scale and identify the section defined as narrow. An authored note might read: “Passage sized for Medium, ten feet long; Large creature: twenty feet of movement in that section.” During the turn, review movement already spent and remaining. If drawing and description disagree, clarify the measurement before resolving passage.
Two Difficult Terrain causes do not double the surcharge again
The same glossary says Difficult Terrain is not cumulative. Adding rubble to this passage does not by itself make each foot cost four feet. Other specific rules can matter: this calculation resolves only the described condition.
Read DMGrid facts and limits and its current presentation. It is a Windows beta for managing campaigns on the PC, with a one-device license and no browser multiplayer rooms. Review the demonstrated workflow and terms before buying. If already using it, prepare a clear measurement and note so moving a piece does not replace the rules decision.