Situated in a chain of hard-stone caverns, Olath Z'Ress stretches for nearly 4 miles. However, it does not cover 4 miles horizontally; the city is based around a huge vertical series of linked caverns, covering nearly a mile from the highest levels to the deepest caverns. Normally an unsustainable size, Olath Z'Rress survives only because of the excellent transport links and geography of the area.

It sits at the junction of three major trade-ways, and these routes are the largest and most stable routes in the Underdark, allowing for large caravans of food to be sent from the neighbouring cities. Huge stockrooms and silos allow for months of food to be stockpiled in the event of siege or supply problems, even for a city of this size. Deep wells provide icy cold, clear and fresh water that in the history of the city have never run dry. There is even some small amount of farming going on inside the outer ring of the city's defences on a few of the levels.

Located against the cavern walls, the city is formed on numerous terraces in each cavern, and generally the position of the house or standing in the house is signified by the height of the dwelling in its own cavern. Every cavern is fortified heavily and is a maze of passageways, gatehouses, fortified guard rooms, moats and traps. Though attacking armies have captured parts of the city in its long history, the city as a whole has never fallen.

Trade routes enter the city on several levels, controlled by different houses that are responsible to the ruling council for keeping the city well supplied. Routes out from the city are well maintained and patrols from the city keep the wide paved roads free from trouble for nearly 3 days in all directions.

Comprised of buildings and structures spanning a period of time from just after the first founding to the present age, Olath Z'Ress is a riot of styles, colours and materials. Houses, temples, workshops, barracks, shrines and magical laboratories cram together and vie for space, with everyone fighting to be as close to the central core and as high as possible in their cavern. Other than the libraries, this is probably the best equipped city for research for mundane and magical processes if only due to the wealth of experience and facilities available. Many weapon and armour smiths are to be found in the city, with some of them having artisans trained by fathers and forefathers for many generations. The city has a large population but still has room for visitors in the many taverns and inns that are to be found in every cavern, though security remains tight as the only way for the city to conceivably fall is by the action of agents working from the inside.

The farmers in the area produce small amounts of fresh produce, using this to flavour and expand the diet of those in the city.