Exploration

Rest

The mandatory post-combat rest turn does not count for the one-in-six turns the party is required to rest.1) DMG 38, “TIME IN THE DUNGEON”.

Dungeon doors

See Door.

Dropping items

There are no official rules for this. The following system is recommended:Ex

Dropping items can trigger saving throws, especially if they are ceramic or glass. Dropping a torch has a 1-in-6 chance for the torch to be extinguished. Dropping a lit lantern has a 5-in-6 chance to ignite the oil as though a lit flask of oil hit the point of impact.

Falling damage

Falling damage is 1d6 points per 10’, not cumulative.2) PHB 105, and DMG 53 in the flying rules. Some say it’s cumulative. We prefer the linear. High-level characters should have a shot at surviving great falls, it’s a fantasy game. If you use cumulative instead, 30' fall means average of (3.5 * 6 = 21) damage, which is enough to auto-kill 3 max-HP trained men-at-arms. It is also impossible for a regular person to survive, when on earth a person can survive a fall of greater than 30'. If the DM wants to create a falling hazard, they can just create a higher cliff or a deeper pit. It's much harder to go in the opposite direction (30' rooftops will always be 6d6 damage; you can't reasonably make houses shorter, but you can make pits deeper). More info at https://deltasdnd.blogspot.com/2009/06/oed-environment.html.

Surface hardness

The DMG advises that damage can be adjusted based on the landing surface, but doesn't provide advice on how to do this. The Heroic Legendarium has some examples on how to do this.

Thief-acrobats

The examples of falling damage in the UA thief-acrobat must be adjusted, since they use cumulative damage.3) Those examples need to be fixed either way, since they mistakenly ignore the rule that falling damage is capped at 20d6.