Fantasy RPG heroes spend a lot of time striding dungeon corridors that are 10' wide with ceilings that are 10' or more above their heads. There is generally plenty of room to do some maneuvering. Real life "dungeons" seldom offer such luxuries of space.
A few situationa that follow have examples of LARPing experience and the terrain features mentioned, I gernally call this semi-real-life as the weapons and armeo still aren't generally as heavy and restricitve as real gear).
The sizes of corridors and doors and heights of ceilings can do a lot to provide players with a wider range of decisions in equipment selection, tactics and even character races. I'm inspired by previous gaming experiences, "Cities of the Underworld" on the History Channel and home repair I've been engaged in of late (crawling about under my porch). Things just aren't conveniently built to make life easy for men about 200 lbs in wieght and 6' tall to maneuver about under things.
A Few years back a small dungeon complex in my game was about a yard wide and 4' to 5' high. After the whole party trying to muscle it's way into the complex the (very large) party sent the small folk in the party down into the depths to sort things out.
Corridors but 2' wide will have prove ultimately unnavigable to people with large back packs, bulky armor and larger weapons. Speeds will be greatly diminished and combat options decidedly limited. It's an excellent situation to send a gnome of halfling adventurer ahead of the party.
People tend to build things that are barely just big enough for peple to navigate a goodly amount of the time. Imagine how tight traveling could get if the locals were only 3' tall. Treasure chambers, redoubts and escape tunnels would surely be off limits to the typical adventuring party.
Narrow door ways slow down how many people can pass through the portal at a given time. A low doorway forces the person passing though the portal to bend and provide advantage to anyone defending the portal against intruders.
A murder hole adjacent to a narrow/low door should prove to be more effective against the intruder with restricted movement.
(LARP: I've stood on one side of a door way with only a pair of other folk and was abel to fight off an increddible number of opponents that literally filled the doorway with weapons but had great difficulty passing through to harm us, suicide tactics and magic were the only things that allowed the enemy access.)
The height of ceilings can have a lot of impact on travel and combat within a room or tunnel. Low ceilings clearly force one to duck down to pass through but they also limit the effectiveness of large weapons which can't be swung effectively with the low ceiling. The center of a ceiling may be higher then the sides, only those moving through the center and fighting within it will have optimal mobility. Small defenders would be able to move more quickly about man-sized foes if those men were to keep to the center of a corridor with a arched ceiling.
Flying beings will be a distinct disadvantage the lower a ceiling the less room they have t maneuver, they may be challenged in a traditional dungeon chamber but lower that ceilign further and mobility is threanted.
A change in the height of ceilings as an intentional defensive feature is very effective. A low door could then lead to a low portion of the chamber beyond whch forces one to continue to stoop, defenders beyond the lowered section of ceilign would habe full mobility and decided advantage afgainst intruders.
(Larp exposure to the lower ceiling: followign the entry into a "dungeon" we discovred the way blocked by a short but wide segment of corridor that was only 4' high, o the other side stood a small number of defenders in a chamber with a high ceiling. It was a very tough fight tying to stoop down and bring our weapons to bear against the polearm equipped enemies who seemed to be able to poke at us with impunity.)
The height of a corridor applies as it does for all ceilings but it will also slow movement and adds t the atmosphere of oppresion for those trying to pass through them. Men can pass each other in a 5' wide corridor whne walking but one man can easily block the corridor in combat and even narrower corridors greatly limit which weapons can be effective (or even possible to carry around corners).
It's not uncommon for coridors leading to shrines or other holy places to force man0sized folk to stoop and even crawl slightly to add to the majesty of the holy space beyond and to make the person traveling the corridor to be humbled before they gain access.
Worker comunication and travel corridors to provide service to areas of a complex will only necessarily be wide enough to allow travel from one point or another by a single file of labourers and will not aid an aggressive attack force, travelign through a low and narrow corridor in armro and with a shield may indeed be impossible in such a space.
The steps one tread on a staircase may be designed to restrict speed of travel and ease of access. A person is slowed traveling up or down a shallow set of steps with a severe pitch. Little folks may be more able to travel such a staircase but larger folks will be at a disadvantage.
Spiral staircases can also be built to diminish the effectiveness of weapon used from those either ascending or descendign the staie depending on the direction the stairs turn again giving the advantage to thge defender.
Intnetionally tight and small spaces much smaller then an ordinary door makes the ever popular "kick the door in and charge " style of dungoen riomping all but impossible. A clothed adult male can pass though a 18" by 12 " gap but thee is no chance someone in any type of armor is doing such a thing.
(Larp:In the dungoen in th eprevious example the party I found myself with stumbled into a chamber where a pair of warriors were doing battle with a air of undead beings that hopelessly outclassed our capabilities, we were fleeing a pack of goblins all seemd lost when one of the memebers of my party spotted a tiny crawl tunnel and everyone jumped in, I followed in the rear beimgn the most capable of holding off the undead long enough for everyone else to escape. The hole was small but we all splipped in quickly. Halway down the corridor I discovered it had gotten narrower and I was stuck as I was alos the largets memebr of the party. It took me a while to relaxe and figure out how to wiggle on.)
How to use this stuff. It all depneds on the game system and your playing style. Weapons could be outrght resticted or be penalized in to hit or damage chances if they are too large. Defenders could gaina bonus to attack vs intruders and small folks may be unhindered when larger folk most certainly are. I worked up chart with sizes and modifiersfor dungeons in the past but have yet to fidn an optimal set of modifiers, it's likely best to note the poetential hiderances and go with what feels right.
Keep track of size of features within a dungeon and all of a sudden gmones and halflings look wise and viable choices in tunnels 6' tall knights couldn't bring their weapons to bear against opponents.