The Rat Warrens is a special mini-level, interconnecting several levels and sub-levels of the Inner Ward and Upper Dungeons. These tunnels are irregular and cramped. The smallest demi-humans, gnomes and halflings, can fit easily but larger player characters, including dwarves, must remove bulky armor. The tallest player characters, including elves, half-elves, half-orcs, and humans must crawl through the passages or travel in a bent-forward shuffling manner. Size large creatures simply will not fit. Refer to the chart on page 38 of the Player's Handbook, WEAPON TYPES, GENERAL DATA, AND “TO HIT” ADJUSTMENTS. Many standard weapons carried by adventurers will be unusable within the warrens due to space concerns.
Because of the space restrictions, medium sized characters will suffer -2 penalties to “to hit” rolls and saving throws while in the passages, but not in the rooms. Rats, even medium sized royal ratkin, are used to the warrens and suffer no such penalties, although intruding monsters encountered as wandering monsters might, at the Dungeon Master's discretion.
The tunnels are carved and chewed from the earth and stone. The floors and walls are earth or rock with occasional sandy areas present. Droppings are commonly found, as the rats and ratkin are relatively indiscriminate when it comes to relieving themselves. The passages are generally only three to four feet high. Portions ascend or descend rapidly, therefore numbers are given next to the passages on the map to indicate depth below the Ground Level. Dungeon Masters should explain to players that the tunnel suddenly ascends or descends rapidly in several places, requiring climbing up or down. In order to avoid confusion with the numbers on the map, the encounter areas are lettered instead of numbered. Room heights are given in each room description.
The Rat Warrens directly connect to the Inner Ward Ground Level, the Cellars, and the Sewers. They also connect to Levels 1 and 2 of the Upper Dungeons.
The rat warrens is the domain of brown ratkin and their servants, the giant rats. Brown ratkin are brown-furred and larger than giant rats, although most are still in the size small range. About half of normal ratkin wear clothes of some sort: a pair of trousers, a vest, a belt, or a fitted leather cap, for example. Patrol leaders and guards wear military uniforms that would not be out of place in a Napoleonic army. Guards wear blue and patrol leaders wear red. Guards generally stay in one place, and are placed to protect something. Patrols are usually composed of a uniformed brown ratkin patrol leader and several giant rats.
The royal family, especially the beastly King Trewkins, rule their rat and ratkin subjects with unquestioned power. Unquestioned, that is, except for the rebellious bastard Sarlomew (Room M) who lusts to usurp the throne for himself.
The royal family consists of the king (Room X), his rather fey queen Hilgreta (Room AA), Prince Hvool (Random Encounters Table), and Princess Fidget (Room Z). The king and prince are solidly within the low intelligence range (the king is illiterate) and it is the queen that provides most strategy for the warrens when faced with repeated incursions. She should be treated as highly intelligent, and will make reasonable adjustments to security if faced with repeated aggression. She will place extra guards at choke-points, add mechanical traps of her own devising, and inform the subjects to face enemies only when they have clear numerical superiority. She might use her contact other plane special ability to good use. The warrens have been invaded on several occasions before by ghouls, giant weasels, and worse, so she has some experience with defense.
Each of the royals is noticeably different from normal brown ratkin. For example, the princess has wings and the king has three heads.
If characters wish to negotiate with the queen, they may meet with success, especially if they have shown clear superiority in combat or magic. The king is a ball of rage and cannot be reasoned with when he is alone. The royal ratkin desire food, wealth, and safety from neighboring monsters, especially ghouls who can devastate their numbers with relatively little effort. They have little to offer, except for some information and perhaps a giant rat guide or two. As is usual, success in negotiation should depend on reaction rolls, player dialogue, and the Dungeon Master's evaluation of the encounter.