Kobolds seldom make use of non-subterranean construction not wishing to expose themselves in such a manner the overwhelming majority of their works are tight fitting and underfoot.
The primary entrances to a kobold warren will often be disguised to appear to be natural caves or constructions of goblin or gnomish origin; it isn't unusual to find the gateways disguised as abandoned mine-works. The gateways will be monitored but aren't typically heavily defended as the kobolds have little desire to lose defenders to an initial assault hoping that their tunnels will discourage a protracted assault.
A most distinguishing feature of kobold tunnels is their diminutive height and width. Kobold tunnels are seldom wider than is required for a larger adult male kobold bearing a load. Transit tunnels frequently used will have side passage to allow kobolds to wait while others pass, there are quite elaborate rules that establish who is to wait when and where in such chambers failing to surrender progress to a tunnel to another of higher passage-rights is a serious infraction in kobold society.
Most kobold tunnels are dug simply through the natural materials of the region they are built in but some will be reinforced with barrel-like segments the kobolds will crawl through. Large spaces may be bridged by linked barrel segments to conceal the purpose of kobold travelers; such segments also are an ideal passive trap that will drop entire segments into deep natural pits and chasms if too heavy a load is carried through (such as a dwarf in armor).
If a kobold tunnel is tall enough for an adult human to stand freely it's either a relic, adopted natural space or a killing place designed to trap invaders who will either be peppered with missiles from murder holes or simply sealed-in to die of asphyxiation.
A divepot is a small connecting feature of simple but ingenious purpose. A divepot will appear to be a drainage pit or some other small flooded feature, it is a connecting point however that only offers access to those willing to fully immerse themselves and pass a short distance (entirely submerged) into the adjoining chamber or tunnel.
Divepots serve a dual purpose as a difficult passage and as a barrier to gases, flames and smoke.
Occasionally a dive pot will lead to a deeper flooded passage or chamber, such a feature is a pit for the unwary or a holding pen for small fish or amphibians.
A small chamber off a tunnel side sealed by a simple plug of earth or stone blocks entrance to a chamber beyond that is often little large than the space required for a handful of sleeping kobolds or a minor store of food supplies. If a plug leads directly to a passage and not a nook the chamber beyond will tend to be larger.
Plugs will not always be in the walls of a tunnel, due to the tight spaces in a typical kobold tunnel they may be found in the ceiling and occasionally a floor (more often to the side in such a case).
Kobolds reproduce by a curious combination of live-births and eggs. The live-born tend to be very aggressive and usually find themselves nurtured and raised as the kings guards. Not all kobold females are allowed to reproduce and there is competition among kobold females for that privilege (which carries a reduction in labor thanks to the useful hands of offspring). Mothers will oversee nursemaids in the egg chambers which are wide but low chambers kept warm with specially selected refuse.
Not all kobold eggs hatch and such eggs will be pickled and used as an delicacy among the kobold elites. The preparation chambers for these picklings will be found in ante-chambers right off the egg chambers.
The galleys of a kobold warren are widened tunnels that serve as kitchen and dinning hall. Travelers will be able to pass through as meals are prepared and diners eat what rations they are allowed.
A chamber open on one side to a tunnel. Lip dens often house kobold bachelors and offer a convenient position for guarded defense of the adjacent tunnel.
A shallow den is relatively close to the surface and while there may be incidental residents and guards the main purpose is to house supplies. By placing these supplies near the surface kobolds hope the goods within will serve to satiate invaders.
Far from the entrances to a warren are found the chambers where the chieftains and their guards dwell. Where the young are indoctrinated and worship is offered.
The most valuable treasures will be found in the deep dens proper where they can be watched over and not in the semi-private plug-nooks and antechambers.
The largest places one is likely to find in a kobold warren are the subterranean gardens where kobolds nurture a variety of fungi, slimes and other exotic life.
Kobold living spaces are usually not in close proximity to these gardens as they can hold rather fierce residents.
On those rare occasions kobolds take prisoners they may be tethered or caged within a deep garden.
Kobolds are often attributed as having a vast array of fiendish and clever traps and while they will defend themselves with traps where practical they mostly take advantage of the small size compared to most would-be invaders. It's difficult for a man crawling through a tunnel to avoid a spear striking from a murder hole and kobolds are well aware of that. A kobold warren is a place of habitation and not a fortress despite it's overall purpose of sheltering and defending it's residents.