A few notes on orcish architecture to set them apart from men, dwarves and elves in a typical fantasy campaign.
The most common orcish structure is a a den. A den is a hole in the ground dug from the surface. They will typically be a tight crawlspace descending no more then 10 or 20' with a 5-20' diameter space almost high enough for orcs to stand upright within. A den may have a less obvious exit-way if it is old enough to warrant the work. An Orc Den built near a tower will often have it's primary entrance facing the tower.
an orc run would appear to be the entrance to an orc den but it is wider and higher allowing orcs to enter quickly and find their way to a broad tunnel leading perhaps as few as two dozen yards to as many as 200 yards away. Orc-runs are used to facilitate escape and ambush. Some orc-runs lead to tunnels that will lead to multiple orc-runs and exits.
Only poorly supervised orc tribes will allow orc-dens to connect directly to an Orc-run.
This is a shallowly constructed orc-den with a means to view the surface, meant as defensive works and not for continuous habitation. Sometimes an orc-hole is clearly raised above the nearby ground but may also be incorporated into a hillside to appear natural and may look like a pile of stones to the unwary. Orc-holes are usually found only near established orc-holds. Orc-holes will not connect to an orc-run but a number of them may exit closely to one.
An orc tower is a look-out tower built by orcs. It will appear ungainly and insecure by human standards but orcs have little trouble ascending to the peak where as many as three or four can sit sheltered from the sun in a nest-like bole or even in a small replica of a mannish tower-turret. Orc-towers are built mostly of wood but wil on occasion have a base story of piled stone. On rare occasion an orc-towers is built alongside a dead (or dying tree) to serve as added support and camouflage and may be very tall.
A orc pit is in wide hole in the ground. It may have started out as a den and been enlarged to the point the roof was collapsed intentionally to provide more space from immediately prying eyes. Orc pits will serve to hold prisoners, work-beasts, and non critical workspaces such as kitchens and abattoirs.
As a pit is used more and more side spaces will be dug into the pit sides. As the side spaces become more populous or more frequently used the pit itself may be semi-abandoned and even covered over to trap the unwary who will find themselves falling into he midst of a number orc-places.
Pit of Woe-
A pit of woe is a deep difficult to scale pit where victims and wounded orcs are tossed to amuse orcs during times of plenty. The upper edges of a pit of woe have a variety of spikes and stakes to discourage anyone attempting to climb out (along with the occasional predatory beast that finds it's way into the pit). Being thrown in a pit of woe is a disgraceful death for an orc and great comedy for it's brethren who delight in the cries of anguish and hopeless battle from the depths of the pit.
This is where the remains of orcs are thrown during times of plenty or when the bones have been picked clean by their fellows. The upper edges of the pit are much like a pit of woe but also discourage entrance of wandering undead.
shallow pits built near an orc-hold meant to be defensive works. These its will have many sharp rocks and spiked sides and are likely to collapse in on nay trying to scale out once accidentally falling in.
While orcish engineering is seemingly crude to men it is not foolish and reckless to orcs and an established orc-hold will begin to sprout chimneys of earth and stone to lift away smoke and enhance ventilation of the space below. Those familiar with termite mounds have noted similarities with Orc-Chimneys as older chimneys will have multiple passage for smoke and air to pass through and even side chambers and tunnels if large enough to aid in defense of the Orc-hold.
Some Orc-Chimneys are often raised directly above pits as a cap but this is not a firm rule.
A ring of Orc-chimneys may surround a hollow that conceals a very large orc-hold. With age the space between the chimneys of such a rung are often filled in with a host of materials and debris which serve raise a hill and conceal the presence of the orc-hold.
A collections of orc-pits, den's, towers and chimneys that serve as a combination orc settlement and fortress.