"Here too, the role of the "Saturday Night Special" cannot be overemphasized. Aside from the deliberately or randomly determined "normal" contents of Underworld areas, it is interesting to develop large complexes inhabited by special beings. These should have special histories, and players should hear legends of their existence on the surface. Their abilities and treasures should be individually devised, since these add interest and spice to the game."
So, I dug into the Petal Throne PDF, and found this:
An Underworld should consist of a number of levels of passageways, rooms, catacombs, shrines, tombs, etc., etc. Each level is drawn on a sheet of graph paper (10 squares to the inch provides sufficient room to develop large temple or tomb complexes). Levels are interconnected by stairways, sloping passages, chutes, vertical shafts with or without ladders—etc. Levels need not be exactly one on top of the other, nor need they all join neatly: i.e. one may have a level off to one side which is approachable only by a stairway down from some upper level and which is not connected to any further upper or lower levels, Thus, the Underworld of Jakalla has a very extensive first level, drawn on a 17" x 22" graph paper. Stairways and other types of passage lead downwards from this to other levels, but those levels themselves are only occasionally interconnected. Certain passages branch off to tie in with still other Underworld complexes; some of these connector tunnels run for miles, being survivals from the ancient pre-cataclysm underground transport system.
It is much more realistic and desirable to have an Underworld developed upon logical, "scenario" lines, with large complexes of tombs, temples or other contents carefully worked out. These can be cut off from one another, of course, by empty labyrinth areas or by randomly selected regions.
Further, about scenarios:
Countries, parties, Temple factions, nonhuman races, etc., etc., all will have objectives of some sort, and the referee should sketch these in... Thus, players will encounter members of different factions within the Imperium, various foreign agents with schemes of their own, individuals with a variety of plans and goals, nonhumans, and other beings.
This makes a Tekumel underworld sound very different structurally than an OD&D dungeon (or, at any rate, an OSR megadungeon):
- a HUGE first level—drawing on 17" x 22" graph of 10 squares per inch
- a limited number of lower levels
- most lower levels connect directly to the huge first level, with only limited connections to each other
- long "trunk" connections to a network of other dungeons
More interesting to me is the classification and arrangement of different types of spaces within a single level:
- Saturday Night Specials, which consist of:
- rumors or legends the characters hear before finding the special
- a unique monster or monster type
- a large complex
- unique treasures with a history
- Scenario areas (where factions pursue their goals)
- randomly generated or empty areas that divide the Specials and Scenario areas